They should absolutely have their own bedroom, not to mention a bathroom each and preferably their own swimming pool

There is nothing wrong with sharing a bedroom, and I find it hard to believe out of everything you could feel guilt over, your friend is trying to make you feel guilt over that. Where you may find you have some issues with is when the baby is young and waking at night, but you could easily have them in your room while they are in a cot and move them into a shared room later. HTH.