Based on the comments--it seems space will be a nicer, but squishier version of all star? no?
I am a family of 6 now, but when we were 5 with one of those under 3....small spaces get tight.
When I traveled as a teen and did Poly Concierge with a family of 5, it was tight.
Since you are the "child" in this scenario and not officially the owner, I'm guessing you are very concerned and that dad just isn't going to listen. Personally--I'm tempted to just say, discuss it with mom logically and see if mom can't twist dads arm. Once you have said your peace, just let it go and travel peacefully regardless of the outcome.
Sometimes parents have different ideas of travel and don't want to listen to the well meaning almost adult. BTDT.
