Inherited Tenant/Lease Question - Adding a new person

[Joe Pozzuoli]

I inherited a tenant in a duplex that has 3 people living in a rather large upstairs unit (used to be triplex so it is 2 combined units). They are wondering if they can add a 4th. The space can handle it and  I would most likely charge $250-$300 more in combined rent/utilities.

Looking at the lease they signed, how would you read the attached clause?

-Since the 4th person is not named on the lease, I can add an addendum to add them and charge an appropriate amount

-If I let them add a tenant, I can only charge them $75

-I can tell them no but they can still let someone stay there and just pay me the $75 (and I would have no recourse)

-Something else that I am missing?

I have guest time-limit sections in the leases that I write but this one does not have one. The only clause mentioning additional people is what the photo shows.

I was thinking that I could also possibly (if they agree) draw up my own new lease with all 4 names and the new amount but was hoping get some feedback on the current clause since it is a bit gray.