My question is can I legally modify the lease to add the 2 additional adults and increase rent by $600/mo? 

Always single females with children. 

If I were you, I'd rent to teachers or staff, meaning adults. 

All adults have to apply and give IDs so you know who is in your property. 

I’m a single mom with adult children and wanted us to be close and build homes in the future.

If you connect with a elderly homeowner who wants to learn more, if possible, make sure they have a younger/responsible adult that they know and trust to avoid bad optics.   

They care about the occupancy and financials a lot. 4. if you are going to run a owner occupied business out of the property such as adult care facility and you are considered 51% owner occupied you can do 20% down and really good rates. 

Since sharing opinions is the entire point of these forums, I'm going to share MY opinion below in the hopes of having a genuine, civil, adult discussion with some other folks who might want to chime in.

All paperwork to the tenants should also state that All adults on the premises  have to qualify for the new rents as well as what ever new clauses that you want in there. 

I'm a 29-year-old single female currently transitioning out of the military, and I'll be relocating to this area in late April or early May.