A friend's issue/something I should know

[David Thurman]

A friend (T) of mine is about to move into a newly purchased home with his long time girlfriend (D), her mother and her mother's infant daughter. T and D have lived together for about 3 years in an apartment. D's mother is buying a home under her mother's name (D's grandmother) due to credit issues. The mortgage payment is more that 50% of D's mother's monthly income making it "impossible" for her to afford without T and D moving in. I told T that he should have some equity in the home himself since the couple will be paying for half of the monthly mortgage payment. On top of that T and D will need to watch D's infant sister when her mother is at work. I was thinking of a sweat equity type of situation but I don't know how he would go about getting that arranged or if D's mother refuses it how he could legally stake a claim to the property since he will be paying 50% of the mortgage payments and at least half the babysitting responsibilities. I am not 100% sure if D's grandmother will be the sole owner of the property or if D's grandmother and mother will have a 50/50 ownership or if D's grandmother is just a co-signer of the loan. I look forward to finding out your responses so I can inform him of what to do and educate myself on what to do in situations like this. Thank you.