^^ what Bogeyface said.
My mum had to share a bed, never mind a room, with her 80yo grandmother!
It's also a cultural issue - the children in the large Asian families I know all share rooms, in fact seem to think it would be odd and antisocial not to. A bit like our horror of cosleeping, the idea that you must have a sacrosanct sleeping space of your own is very much a postwar Western luxury/fetish. With house prices at current levels, and pensioners sitting in big family homes whilst families struggle to afford high mortgages on small houses, I don't think anyone should think that children are somehow losing out by sharing a room! Most young families I know in London in particular have their children sharing rooms, simply because another jump up the ladder to get an extra bedroom is costing more than 300-400k in most parts of London - unaffordable!
OP I think that the fact your boys are twins makes it different to most siblings. As a child I shared from 5-11 with my nearest sibling, but as the age gap was 5 years it got too disruptive for a 11 year-old pre-teen coming up to secondary school to be sharing with a messy, noisy 5 yo who had a totally different bedtime and routine. I think room sharing works best amongst similar age siblings or twins where you don't have any hassle about different bedtimes, fairness, and so on. Twins sounds like they might even enjoy it.
As pp have said, you could perhaps look for a house that could be extended in the future when your kids are a bit older and your DH has had a bit of a breather?
In any case, I think you're right to prioritise your family life and health - stress from long working hours is no picnic, and it can have serious health effects in the long term.