When they were up to 8 & 9 yes they were always sharing a room.(Two boys)...it made them very close.Then once they had their own rooms...no.
But 4 years later, they were back in the same room again, as we moved house.
I feel if both the same sex.....they can, it was a very positive idea we had.
Of course up to 4-5 they still could share, if the same sex......but after that not really fair for them.
Boys like their rooms with boy stuff, and girls ..well we know what they are like :)