Abel is correct that you will pay about $65/month for the software as well, assuming you have more than one property.

In this case their total household income (of the husband and adult son combined) does meet the requirement of being 3x the rent, but how should I apply requirements of good credit for this and other applications with multiple tenants in one application? 

Unfortunately, I have not had much success as I have barely gotten 1 application.

How do you keep track of insurances expirations, taxes dates, equity growth per house, rental growth in your area ? Is there an online platform on which we can do this or do you track this in a excel sheet ? 

However, there may be alternative tax strategies out there that are more applicable to your current situation or property.

I would also research some property management software (e.g.

I used Zillow to list my rental and accepted someone's application however after my few interactions with them on the phone some major red flags have come up and I wanted to know am I under any legal obligation to rent my property to this person. 

No test, no experience, nothing else needed (beyond an insurance policy number to complete application).  

Is there a tool or software that can do this?

@Michael Csrnko1) Make sure to use a pricing software like price labs or wheelhouse to have competitive pricing. 2) Don't always give refunds or credits to guests when they complain to get a 5 star review.