To rent or not to rent?

[Simon D.]

Hi All,

I have a prospective tenant looking to rent my sf house. Tenant is a single mother with 2 teenage kids and a boyfriend. Mother makes around 20k/year with an additional 2k/month from a part time job. The boyfriend makes around 70k/year. Boyfriend says he has his own home but will help with rent. Outstanding auto loans from both parties. Both their credit hovers around the low - mid 600's.

Rental = $3200/month

Any tips/advice for setting up the lease so that I can ensure the boyfriend will be liable for the rent? 

Suggestions on whether or not you would rent to this tenant?