Yes, of course it will be a legal contract!
My question is how do we (wife and I) make money?
Say the house is $500,000:
Down payment (10%) - $50,000
Monthly Mortgage - $3,000
Monthly HOA - $300
So, if we choose to "split" the house, and each put up 1/2 the down ($25,000 each), and 1/2 the mortgage ($1500), and 1/2 the HOA ($150).... seems fair... until... they live there...
We are both shelling out $1650/month, and they live there, they are getting a better deal. So, I "charge" them rent?