Screening applicants with a co-signer

[Russell John Walsh]

I may choose to vet a young couple , both  currently off their jobs due to being non-essential. They want me to take a co-signer.

It seems, I would fully screen  the two people, and the co-signer

Would I ask for tax returns to prove consistent employment? What other credit references besides standard credit and background checks? 

I would give the co-signer their own application as a co-signer only? Same standard credit and background checks? Additional credit references for the co-signer? Should I have the cosigner prove with tax returns and reserves if they are self-employed? 

* Also , since the couple can't stand alone qualify I am thinking to ask for the deposit to be twice rent, with move total financial consideration to  be $3100 plus first months rent $1550, all  in  a cashiers check at signing. 

I am not desperate to rent, so I am not willing to soften those terms which are legal in my state. Am I on track here? 

Thank you,