tenant application questions

[S Harper]

We have only placed tenants 3 times, with one of them not working out very well (so I am gun shy).  There are enough small things that bother me that I thought I would seek input from more experienced landlords.

Single dad (with 2 85 lb mastiffs), his 19 year old son, 24 year old daughter and her boyfriend.  Would you recommend having all four sign leases?

Dad's gross = 1.5x rent

daughter's gross = said 1.5x rent, but am waiting for her to provide 1099s to confirm as she is an independent contractor

son and boyfriend will be another 1.5x rent total, but haven't verified income or run their credit checks yet as I have questions about the things I have found out so far. 

Dad and daughter have credit obligation minimum payments over 20% of their gross pay, our rent would be another 25% of gross.  In your experience, is this a workable set of obligations? 

The dad failed to include a car loan on the app (he said he is co-signer on another son's loan and forgot about it). 

The daughter failed to include a car loan on the app (she said she is co-signer on her boyfriend's car loan and didn't know if she needed to include it as he pays the bill), and told me $100 in credit card obligations vs the actual of $328.

They have credit scores of just over 600 for one, mid 500 for the other, and have no late monthly payments on the credit report. 

I met the dad and daughter and they presented themselves well (and no red flags on their facebook pages).

I am still waiting for their landlord to call back.  They were paying quite a bit less there, but were there for 5 years (they said they are leaving because landlord is selling).

With my limited experience these small things all make me concerned, and I don't have enough experience to tell if I am over-thinking.

Thanks for any input.