Seeking advice on a co-signer on a lease

[Steve Balinski]

Hello everyone, I'm a small investor looking to fill a unit in my 4-unit building.

Criteria: 670+ credit, income 2x rent. 

The 2 people who will be living there don't meet either, but one of their fathers is willing to co-sign, he meets all criteria favorably.  I've never had a co-signer before.  The 2 applicants are in their 40's, have no criminal history, bad credit, low income (not career based jobs), 1 of them has 4 collections (*All under $200 and closed out though).  My fear is if they're not responsible with their credit (low dollar amount collections so I'm not looking to much into that), don't have career based jobs, are my concerns valid that they're most likely not responsible enough to live in my property? (I have pretty high standards)