I'm wondering if maybe you shouldn't be communicating less with them ... Though you don't stay the night when they are there, you are still there for all the rest of the time. In other words, they get very little time alone with their father and he is, after all, the one they come to see. Try stepping out of the picture for at least one of the days during the weekends when they are present and see if things don't get better. 

I don't think forcing yourself on them (which is what your bf seems to want you to do) is the best approach. It's easy for your bf to criticize ... he's known them all their lives, you, on the other hand, are only just starting out with them. 

Bottom line - don't try too hard... it seldom works.

If you try too hard to "bond" they might think you are trying to replace their mom. That will backfire on you especially with teens, they don't even want to much with their bio parents. If your bf doesn't communicate with the teens himself he is using you as a buffer. That's not fair to you, don't force a relationship on them. 

I have two teen skids at home. We aren't best friends but they are polite and pick up after themselves. They open up more to my younger sister at family events than me and I've been around a decade. 

Heck, I agree with winterglow, you should do LESS. When I was a skid it was my major complaint with my stepmom--not that she was unkind or bad at all--but I wanted time with my dad.

few things...

1) not only has BF known his kids his whole life, he probably has no experience trying to form bonds with kids who are essentially strangers. Also super common that dads wanna picture one fantasy scenario where a blended situation looks just like a first family. It never does.

2) polite and respectful is great! Many of us with teen SDs would find that a DREAM! Relationships take so so so much time. And that's actually a good thing. If they had no boundaries and clung to you like perfect future stepmommy that would be...weird. Slow and steady wins the race.

3) stepkids are like cats. Or so I've been told. Give them their space and let them approach you when they're ready. Ask those good questions and learn about them but don't push. If they want to pursue more of a relationship, match that energy and reciprocate. 
 

but holy smokes, pleasant and respectful interactions are awesome and totally enough!

Your BF said you need to communicate MORE with them, yet they give you short answers , this shows a lack of interest in you! Call me negative nellie but with SD's I assume the worst. Did he say the same to his kids? Or is the burden on you and you only? That may be a peek into the future, YOU are the problem.

Think about it. If you met a friends or co workers teens would they be like this? Maybe, but more likely if they were showing you little interest the parent , at least a good one, would say after the fact  "Hey insert name____ was asking you questions, you are being short" 

So I agree show less interest and if BF says anything you say I try but I dont want to push it. It takes two to tango hun, they are old enough to at least feign  interest out of politeness.

Maybe its too soon to come to judgement. However you reached out on here so most dang likely your gut is telling you something is off in the chicken coop .

You've been in this relationship for a few months. It's WAY too early to expect anything other than politeness at this point. That they ARE polite is fantastic. Don't push it.

And I agree with the others -- back off and let the girls have a day with just their Dad. This is all new to them too. There's no rush to be a "family." Let it evolve and if all you ever get is politeness, it's still a win.

While I agree with everyone that you need to give them space let daddio and DD's have more time together, maybe big daddy is passing the almighty buck.

It seems he wants OP to try MORE not less. Wonder if OP is a convenient buffer because for whatever reason he does not want to entertain his kids solo, its too much work. At the same time he wants OP to give more because he is a lazy parent. He wants a built in buffer/ nanny. Mine was like that at first, until I finally had enough and made him parent. What a joke, the lil B got worse.

Anyhoo just throwing my two cents in. Hope I am totally wrong. 

I think that people make this process way too complicated.  Rather than focusing on bonding, IMHO the most effective way to manage this process is to focus on the adult relationship and be clear on how  you will be respected within the relationship and by the Skids.  This sets the foundation for future and long term success if the relationship has legs.

Trying to bond is not a defined process, nor does it usually have defined goals.  Boundaries and behavioral standards are simple, enforceable, and keep things simple.

I would say that with teens, you are really not in a bad place for the early stages of this relationship with their dad.   Keep in mind that these young women are probably significantly aware that you and their dad are a couple.   I would not step too lightly around that fact.  This man has kids, he will always have kids, his kids will always be an influence on the relationship you have with him, and they will always have a presence in that relationship.

Don't over complicate it.  Planting your flag regarding the behaviors you will require from them, and from their dad, will stand you in good stead regardless of how long this relationship turns out to be.

Bonding.... is a process.  Don't rush it, don't push it, and don't worry about it.

Enjoy the stage of the relationship you are in and if it evloves into something long term, maintain your position on how you will respected and adapt as events unfold.

Good luck.

Take care of you.

Your boyfriend actullay has no say in whether you need to "communicate with them more". First of all, you've been seeing him a few months, second, maybe HE is the one who needs to communicate with them more.

Their weekends with him are for them to spend time with their dad, not for them to bond with the woman his dad is dating.

Being cordial, doing thing with all of them occasionally, is perfectly fine. But, you are not obligated to bond with them. It may happen someday, it may not, doesn't mean you can't have a decent adult/child relationship with them. Shoot, one of them is an adult and the two of you can navigate your own relationship, no need for him to force it.

What do people mean by "bonding", anyway? Become best friends? Become spiritually connected? Become like mother and daughter? Seriously, I have truly bonded with very few people in my life. To me, that is a depth that just doesn't happen very often. It certainly can't be forced.

Some men want there girlfriends with them when they have their kids as a buffer becuase they haven't bonded with their own kids and don't know what to do with them or how to talk to them.

You do you. If you want to be there, fine, if you want to do your own thing sometimes, and let them have their time, do it.

I will tell you, one of the best ways to get a man's kids to resent you, is to be there ALL of the time.

Haven't read the other threads but what I will say is just don't bother. I have been a step parent for many many years and when they were pre-teen it was a lot easier but I think even as a BIO parent it is hard to bond with your kids from a certain age. They don't want anything to do with you.

A Modern Family (TV Show) Analogy. Teenegers are like sending kids to the moon. You are in constant contact but then they go to the dark side of the moon and you sit there and you just wait and hope that they come through to the other side.

I've given up with one of my step kids. If he doesn't engage with me, I basically don't try to engage with him. I've tried for a long time and now I just can't be bothered, he's like this with everyone but maybe even more uncomfortable with me.

Just be kind and do your best, but if you don't get much back that doesn't mean you should try harder. Just let them get on with it.