Renters planning to sublease

[Jerry Cossack]

I have 2 prospective tenants (a couple) who would like to sign a 2-year lease with the option to eventually sublease.  They are planning on being in the apartment for the next year, then moving for a job for ~9 months, and then returning.  They would like the option to sublease while they are away.  I don't see any major issues as long as the lease has them jointly/separately liable for rent.  They would be responsible for finding the sublease tenant, and I would have the option to screen/approve.  Is there anything else I'd need to account for?