dogsandkids "Our social worker in Stage 1 encouraged us to consider siblings" Did you consider this before your social worker mentioned it?
Do you want to adopt two or is it simply because it was mentioned?
I am sorry to jump in here and please feel free to ignore me... but I'd be more concerned about adopting two children when you already have one. I would say that your birth child could feel quite out-numbered dealing with not just one new child, but two.
Can I ask how old your birth child is and the age/s you are hoping to adopt?
If you really want to adopt two children and the house is largish, I would see about converting the biggest bedroom (possible your bedroom) into two. You could do this quite cheaply with a dividing wall, cheaply compared to building an extension.
I totally agree with Kewcumber "The overwhelming rule is that each child needs their own room. Of course you can always find exceptions to that rule most notably with siblings already room sharing but it is the exception rather than the rule."
itsbeenaverylongweek "I've got to be honest I don't understand why this seems to be an issue these days with BC as well"
I'm not sure it is an issue with birth children, unless they are the opposite sex and older than a certain age (in which case it is fairly obvious why it could be an issue).
For adopted children it might be helpful to think about why their own room is recommended. Although children who have lived through loss, neglect, trauma etc may wish to share a room and be close to each other; at some point they may want and need some independence from each other. Not having their own room would make this harder.
Your adopted child/ren cannot share with your birth child, so if you had two adopted children in a shared room and a birth child in a separate room it seems a bad idea. I can imagine all kinds of jealousy going in both directions.