He was the equity and I was the sweat. 

Honestly, it was a lot of sweat equity in the beginning physically working on the houses every weekend.  

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 put a lot of sweat equity into it, but some times that's part of the game.

I have seen good negotiation skills get 15% of profits with only sweat equity on a $7 million deal.

The only thing I can tell you about 12%+ returns on any assets that does not required you to put in sweat equity/time would be highly risky.

Unless you want to be an agent don't sweat the learning part too much.

So, what is the best way to invest my sweat to get hands on experience before I invest my money?

How do you weigh the additional capital he brings to the table versus the sweat equity I'm contributing.

If not, no sweat!