"?Fathers should not be so quick to change the access to their elder children when they have ?new? families?
But as we?ve said, time and time again, if a new baby were to arrive in a ?together? family, there may well be some changes. But in ?step world? it seems that the step children have ?priority status? and their arrangements CANNOT be changed under any circumstances, whereas in a bio family no one would bat an eyelid if a new baby brought about changes."
Yes, there would be changes but you wouldn't expect the children who lived there full time to go and sleep somewhere else so you shouldn't expect step children to stop over nights.
There have been possible solutions suggested by pps such as a specially made bed for the boxroom/futon/blow up beds. The OP (and her DP) could consider all these first.
OP I know you don't have the money to move to a bigger place but would it be possible to move sideways, so to speak. Could you look around for a 3 bed place where the smallest room is a bit bigger than what you have now? Then maybe the baby could have the small room, you and your DP could have the middle size room and then give the bigger room sectioned off, so they could have some privacy, to the DSC.
You say the DSC are 8 and 10. You're getting married later this year so, presumably, by then they will be closer to 9 and 11, if not already those ages. Then you have to actually tcc, which may or may not take a while, plus the 9 months pregnancy. So by the time the baby is born chances are that your DSC will be, at least, 10 and 12. The baby will be in with you for the first 6 months, then could move into the smallest room to start with. Assuming you conceive first time around by the time your DC is 6 the eldest will be going to uni and you can move who has what room. It could be that before that you'll find that the DSC who is the same sex as your DC will prefer to share with his/her half sibling, on the weekends they are there, to his/her sister/brother.