What can I legally do?

We let an expecting couple rent our basement. Halfway through the lease, they bring his parents to live with them. We share a common walkway to get to the door and they have to pass through our space in order to do so.

We gave them the unit at a heavily discounted rate since they were struggling. Now we feel we are being taken advantage of. Utilities included in rent (which isn’t much). We are taking the hit for this. Is there anything we can do? We tried talking to them but they said they cannot help at all (and suddenly started talking about legality of things when we let a lot of things go). The relationship has soured. Lease ends in 4 months.

What are my options here? Just ride out the next four months? We gave them an N11 that has yet to be signed and served them with an N2 as well just to be safe.