BACKGROUND: Met DH 3 1/2 years ago. He has 2 DS' 4 & 8. He and Dex-W split when she was PG with their DS2.
I have 1DS aged 9. We both have newborn IT 3 weeks (they are also boys!)
DH and I lived in a 3 bed (it was mine) and had the double, DS had the smaller room (still double size) and DSS' had the other double with bunks. They used to come Sat am until Sun pm as per divorce agreement and CSA payments. They would stay extra as well and are lovely boys.
Roll on last year I discover I'm PG then we find out its twins. 
We bought a bigger property (4 bed) with a loft conversion that wasn't a room (something to do with planning?) which we got plans for and is now mine and DH bedroom. Its ensuite with dressing room as DH says I need some female space. 
That leaves the 4 bedrooms on the first floor. One is a large double with ensuite, 2 good sized doubles, and a single. (not box but fairly small) DS has the double/ensuite and DSS have another room each.
ATM twins are in with us (have a cotside on bed and they both fit as tiny and I'm EBF).
DSS' now stay with us Friday after school until they are taken to school Monday morning. DS and DSS attend the same primary. They have things at ours so don't need to bring anything and uniform is washed to start Monday.
Also DSS' come during school holidays for a few days/ sometimes a week if longer holidays - and want to more now they have new brothers.
Now heres the bit DH and I can't agree on. We plan to move the twins to their own room at 6 months. They will share. The 2 oldest boys have offered to share but DH thinks my DS should have his own room as he lives here permantly. I say his DSS' have the same rights.
So my suggestions are: DS and DSS1 have large ensuite, twins one double and DSS2 the other (smaller) double. The small room becomes childrens den with tv/ consoles.
DH thinks the twins should share a double, his DSS' a double and DS has the double/ensuite largest room to himself.
DS' agree with me and DSS2 thinks the fact he gets his own room is great
. The fact DS and DSS1 are similar age means they like lego etc and DSS1 does get frustrated sharing with his brother (4) as they don't really play with the same toys. (have their own rooms at their mums)
DH thinks I'm just trying to be supermum - that I'm trying to please everybody and is worried my DS will feel resentful in the future that he didn't get his own space in his resident house and hid DSB did. 
I know DH is concerned about how much DSS2 gets away with at his mums - he thinks he's spoilt and DSS1 gets a rough ride and thinks maybe its because him and Dex-W split whilst she was PG with him. I think he is worried DSS2 will thinks he's more important because he doesn't have too share and stop annoying his brother. 
AIBU - or does my arrangement seem OK?