Depends on the EXACT terms and conditions of your rental agreement.
NJ is basically a pro-tenant, anti-eviction state so you have to be very careful as to how you approach this.
1 - Does your lease have a duration: from - to date?
2 - Does your lease specify that the rental is limited to the two brothers by name and nobody else?
You may have "rented" to two brothers but, without a specific limitation you might not have sufficient "legal" cause to do anything about the change in occupancy.
Here are the grounds for removal of a tenant:
http://njlaw.rutgers.edu/cgi-bin/njs...1&actn=getsect
Here's the eviction statute:
http://www.state.nj.us/dca/divisions...i/evic_law.pdf
Tenants' Rights Guide:
http://www.lsnjlaw.org/Publications/...antsRights.pdf
The statutes referred to in the guide can be found at:
http://njlaw.rutgers.edu/collections...s.php?title=46
You need to know those laws backwards and forwards. Or, you need to hire a lawyer.

