I'll be away during the summer months. Yes, with your landlord's consent. You must notify us who is in the apartment. Subletting does not remove your responsibility for the rent and all other responsibilities of your lease. Your building manager can supply you with a sublease agreement.
Roommates sharing an apartment are each responsible for the entire apartment.
You do not rent part of an apartment. Also you cannot give notice to move separately. There has to be understanding between roommates concerning who is leaving and who is staying and taking responsibility for the apartment. You should contact your building manager who will help you with roommate problems. The lease says no pets, but I have seen pets in the building.