I agree with OPs plan. Her DD only has one home, one bedroom and I think it is very gracious that she would be so willing to give her space up all the time to accommodate a once a week visit.

You are right, the best thing to do would be to put the two girls of similar ages in the same room together. Now if that means that there needs to be a reshuffle then so be it. Its always a good thing to go through kids toys and books, asking them to decide what they want to keep and what they want to pass on.
Bunk beds are a great way of gaining a bit more space, ofcourse you may have the battle of "I want to sleep on the top bunk!!"

sounds like OH came in to your and bioD home with nothing. Where did Sd's bed come from. Does he pay half the bills?

if not he can go pound sand. It is your home and a once a week slepover does not justify disrupting your BD world.

Smaller room is nursery and larger room is shared by SD and DD. I think it's fine for DD to have more space-she is there all the time. My BS and SS share a room and my BS gets to use more of it. SS has a room at BM's so he keeps most of his stuff there. I wouldn't think that your SD would have as much as DD at your place anyway. What would be the point for one day a week.

Remember if DH has a problem with it he can step up so you can afford a larger place.

I agree with your plan. Your SD most likely thinks of her mom's house as "home" since she only stays with you one day a week. Your BD's ONLY home is your house and it wouldn't be as fair to her to make sacrifices for a child who is there for so little time.

There are also trundle beds that are twin size. Maybe that could be an easier route... it also makes sure the room is cleaned up before bed so there is room for the trundle to be pulled out from under the other bed.

I have to agree that you don't need to bend over backwards to accommodate a 1x a week guest.
I'm in the same situation, SD7 hasn't spent the night in over a year, DS3 has his own room, and we are expecting DS.

I thought taking SDs room back to become the nursery would be a big deal, but since she stopped coming over, it makes total sense. Full time kids should have rooms, visitors don't.

I don't know how things will be handled in the future, I expect her to probably end up on the couch. I don't see disrupting our setup to she can have her own space, her has her own house with all the fluff.

Yes your daughter may enjoy sharing a room, but you never know. I personally like the trundle bed idea the most as its tucked away when not in use, and practical for other night guests/sleepovers.

I realize that she is only at your place once a week, but it sounds like your DH wants his daughter to feel included in your home. When my DH and I married over a year ago, we looked for a house with enough bedrooms for my 2 (who are in college) and his 2 teens (who are with us 50%). My 2 are not home a lot, and I know my requst was probably silly, but I wanted mine to feel like they had a home to come to . My DH was awesome about it and he happily (I think ) accommodated my request. I love him for it! I would have been really pissed if he had sat my kids down and said "Look, you don't live here, so we will not be considering you". Just another perspective.

My mom remarried when I was 10. I inherited a step sister. We had a 3 bedroom house, so mom/SDad had one room, my step brother had another room and my step sis and I shared a room. BUT because she only came once a week, you honestly would never know there were actually two girls in the room. I had a bed, that another bed pulled out from underneath.. I think it's called a trundle? Step sis, really didn't keep any toys, clothes or much of anything there because, again, she was only there once a week. She did have her own dresser and I had my own dresser. Again, other than that, you'd think it was just my room.

you know what YOU want, you know that your DH is going to buck you... so how about make it HIS decision. How about you suggest to him that SD6 and baby share a room, since SD is only there once a week, seems logical right? But then say something to the effect of "It will be frustrating if SD wakes up baby or vice versa, and frustrating for SD who won't be able to be in there when baby is napping, will have to be more conscious of her toys being left out etc. but we'll manage, right honey?" (blinkety blink, sickly sweet voice) I would almost bet money, he will see what a stupid idea this is and will find it a good idea for the 7 year olds to share a room... but that's just it. It will be HIS idea. Men are dumb and they certainly don't like to be "forced" to do something, so maybe some reverse psychology so to speak could work in your favor here.

I see nothing wrong with girls of the same age sharing a room. My stepsons are twins and have always had bunk beds here. We are having another baby, who will have to stay in our room until we move into a bigger place. I'm not going to put a baby in with my toddler, who is an awful sleeper anyway. Kids shouldn't share a room with a baby.