First time here, no clue what all these abbreviations mean, however, for me to google and look for this, I clearly need some advice, a shoulder, or just to vent. Please be gentle.

Husband and I together 5 yrs, married 3. For the record, we met after he separated. I was already divorced.
I have 4 children, he has 2.
2 out of 4 of MY children live with us.
0 out of 2 of HIS children don't even bother visiting.

First problem:
His 2 children live 100% with their mother. 45 minute drive one way.
In 5 yrs they have been to our house twice. Refuse to visit, expect Daddy to drive 45 mins and pick them up, pay for dinner, drive them back. Daughter is 19 and has her own car. Son is 16.
We go to every sporting event, dance concert, everything we can just so he can spend time with his kids (he has no visitations or access - nothing. Kids were old enough to make that decision at time of separation, so no access organised through courts. Any visitations or access husband tried to organise when they were younger were blocked by their mother).

As mentioned, we go to everything we can - even if we drive an hour to spend 5 mins with them. Sometimes he goes alone, sometimes I go too but respectfully step back if needed. Sometimes we have to look up the information so we know when a game is, or a concert is, or other events, because they will not let him know!

They did not come to our wedding because 'they were busy'.
They will not make arrangements for birthdays
They did not invite husband to high school graduation because 'I didn't think you could get time off'
They did not attend husband's 50th birthday because 'they were busy'.
They will not acknowledge our marriage in any way.
They will not see us for Christmas, despite trying to arrange it every year.
Last year, we organised Boxing Day lunch instead. Last minute phone call from daughter "We're not coming, I'd rather go to the Boxing Day sales".
Year before that, they were supposed to come Christmas eve, but another last minute phone call to bail out.
Every Christmas the same deal...

I think you can see where this is going. So I go around in circles asking myself questions.

Is this because of me? They're polite when they see me. Their Mother has even thanked me for the way I treat them!
Is this because he lives with my kids and they're jealous?
Is this their way of punishing their Dad for leaving?
Is this their mother's influence? Parental alienation!

Second problem:
Whilst my husband sees all this, he won't act on it. He thinks if he pulls out of doing things for them, then they won't see him at all. (Probably true!) He pays for daughter's phone and private health cover. I argue that she's an adult and works and should be paying them herself. Especially considering 3 of my children are adults and don't get theirs paid for! She regularly goes over her data quota. Who pays for that? Daddy! I try to tell him to give them consequences, draw boundaries etc but he won't. He's scared of losing them altogether. I argue that it can't get any worse than it is and that they need to respect him.

The last straw:
My FIL is dying with Leukemia and may not make it to Christmas. We've driven every Saturday to go and see him. 6 hour round trip. As this will be his last Christmas, we're spending the day with him and MIL. I've sacrificed seeing my family, but they understand. So, once again we've asked his kids about Christmas, and would they like to come with us to see Grandpa one last time? They haven't seen him in years (more than 5). No answer regarding Christmas, but daughter promised to go with Daddy another time. They organised to go yesterday, but I'm sure you know what happened. She bailed at the last minute AGAIN!! Her Grandfather's dying wish is to see his grandchildren one last time. So, instead of calling them out, Daddy says "That's ok, it's up to you". I'm saying "THAT IS NOT OK!!! 5 Christmases without your kids is NOT OK!!! Not bothering for significant birthdays, weddings, graduations is NOT OK" It's falling on deaf ears. He hears me, but he's not listening. I'm devastated by this. Yesterday I was so distraught it made me sick.

The only disengaging I can do is to refuse to go to their events. Which I've started to do. But to be honest, I don't think they care if I'm there or not. I can't make my husband stop paying for their private health or phones, because they're in his name and I can't access it. I love my husband with all my heart and unfortunately he's a big softy. He compensates not seeing his children by giving them everything they want. You should have seen the argument when I said we weren't buying precious daughter a car! But seriously, this cannot continue.

Please don't say "tell your husband to grow some balls". Yeah, I know he needs to. He knows he needs to. But how and where do I plant the ball seeds to encourage them to grow??

Bottom line: they'll only see him on their terms and only contact him when they want something. I understand his need to maintain a relationship with them and I fully support that. But when it's not returned, where do you draw the line? It would be easy to give in, but I think it's admirable that he keeps trying. I'm just the bystander who picks up the pieces every time he falls apart.

Any advice graciously accepted.