Unfortunately house hacking is kinda out of my reach.I have a 3 bed 2 bath primary that my wife and I live in with my 2 adult sons,which need to start investing in there own home by now lol,20 year old and a 23 year old.And my wife loves animals so some of those too.So I come with a lot of baggage to house hack I believe,unless there is a way I am not aware of.Sounds like your off to a great start,keep going forward!

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

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.   

Also, due to KC mayor creating this ordinance, which to highlight and summarize includes:bans discrimination against tenants based solely on:"-Source of income from an occupation, including gig work or paying rent in cash-Use of public programs like Section 8 Housing Choice Vouchers, disability checks, or social security-Poor credit score-Prior evictions and alleged damages older than 12 months (less than 12 months can be a basis for denial)-Prior convictions or arrests (sexual and violent crimes are excepted, a landlord can still deny based on these convictions)-The ordinance also requires the city to proactively scan for rental ads using discriminatory language like “no Section 8” or “no past evictions”.

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. 

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. 

The fee is advertised publicly for all to see, regardless of age, gender, race, sexual orientation, accent, or whatever.