Newbie tenant screening question

[Michael Doub]

I just finished the rehab of my first BRRRR and am screening/selecting tenants. A young engaged couple applied and completed credit and background check on my cozy listing, but only her information was there because he does not have a SSN. This couple was referred to me by my contractor who is family with them and basically said he would co-sign lease for them if they ran into trouble/difficulty paying rent (i put no real value in this as it is the tenants responsibility not someone elses). How should i evaluate the worthiness of these potential renters, if i should at all ? He is the main breadwinner in the relationship. Or, is this an easy decline?