Tell him he can move out voluntarily and walk away without any additional charges, or he can be kicked out the hard way and you'll charge him for every dime owed.

A couple additions that may sweeten the pot for you.At "4" when you convert the rental into your new primary you may want to sell your current rental since you will get the first $500K of profit tax free. 

Many people at that age figure out that it is easier and actually more fun to have a part-time job to add to the pot over the retirement years than it is to worry about large capital investments like a single rental. 

All marital assets will be measured into the pot before the soup is divided - IRA and retirement accounts, stocks, savings account, cars, value of the primary home and other real property.

There are a lot of costs that increase when you have kids and combine that with the fact that you are young I would not voluntarily put myself in a position where you are decreasing your income and your ability to get loans as both are vital in growing a real estate portfolio. 

I wasn't sure if a variable rate or a fixed rate would be better but compared to hard money and private money loans if I can keep it under 7-8% APR and under 2 pts I'd be happier than a leprechaun with a pot of gold!

If they over leveraged on rent and lost their job where they could no longer afford your rates would you voluntarily accept less than the contract out of the kindness of your heart? 

Insurance had confiscated the oven because they had determined a specific burner had been left on with a pot of oil on it.

Would you guys shrug it off and just hope they pay rent in future or would you guys bring it up and stir the pot?

on the contrary takes much far less skill to manage stocks , look at the amount of wealth managers out there  ,  not saying that stocks are bad but it cant be compared to STRs , an STR doesn't lose value when mr musk decides to smoke pot :) .