They've just moved to a 3 bed so I'm assuming the new baby wasn't planned. The twins just got their own room but now they want them to share again so the baby can have a nursery??
Surely Topsy and Tim don't need to share yet as the baby could go in with mom and Dad for a year and then share with Tim?
I know they're only 6ish but Topsy will be going into puberty in a few years.