1st time landlord: Thoughts on applicant

[Johnny Sung]

1st time landlord here and looking for some insight.

I currently have a 3 bed/2 bath home up for rent in southern california. Rent is $2100/month. Great area, would say area is A with this being the B neighborhood.
The detached garage is going to be converted into an ADU later this year. It has been listed about a month and I get a lot of initial interest but not many qualified applications. I am currently considering this application.

3 co-applicants/roommates, 2 are related bro/sis. Combined their gross income is 3.6x rent. 1 great credit score (mid-lower 700), 1 mid (Mid 600 no credit history), 1 bad credit score (mid 500, balances owing on closed accts but no collections no open accounts.) Background checks all come back good. Able to verify all employment and current landlords all give good references. Unable to get a hold of the prior landlord for 2 of them for a reference. Maybe I am overthinking it but I am leaning towards approving them. 

Any advice would be appreciated.