Anyone over 18 fills out has to furnish their social security and driver's license numbers, and pays a fee for a credit / background check.

Quote from @Jake Handler: For anyone that has been a buyer or seller of a seller finance property, what method of payment and tracking did you use for buyer to pay seller monthly? 

I would only use the heloc if you plan on cashout refinancing one of the properties to pay it off once the rehab is complete. 

Pay everyone more than what they make now at their construction job, be kind, and give them bonuses based on completion, and they will never leave.   

Also you're probably not really paying much off on principal on a fairly new loan. 

We've since increased their rent to market rate, and now we're experiencing late payments.Family Member as Tenant:Issue: Our family member is behind on rent for more than 5 months, with a rate below market due to their relationship with us.Behavior: They have made excuses about financial struggles, yet have been seen treating their new girlfriend to fine dinners and outings.Impact: Both tenants consistently pay late and have shown complete disrespect to us, the property owners, despite efforts to ensure their happiness and success.We'd hate to impact our relationship with them, but right now, they're hurting us and our pockets. 

If you do have a TX LLC just to hold a TX property, you still have to register in CA as a foreign LLC, which still means paying the CA LLC tax.

Furthermore if they are always paying they probably will stiff you in the end if they know they aren't going to get the deposit back. 

Do they pay within 5 days of the first of the month (in some states that is not late)? 

That's disappointing, I'm here to learn and would happily pay for it if I used it extensively.