Cherry, are the booster seats the 4yrs+ ones? They might fit with a baby seat, but it might not! It is notoriously difficult to get three car seats across the back of any car .
You might need a multimac too! I have been looking into it and the infant carrier does appear to come out - you just pull a lever and it comes free. I have applied to have a fitting session, someone comes to your house to give you a free demo! Unfortunately our Honda is not on the fitting list so not sure it will fit, but fingers crossed, I would love it not to have to get a new car.
Caz, that's great! Sounds like you had fun.
Vix, I don't envy you with a 3dr car but you'll manage.