First, you need to understand that there are 2 agreements here: one is the contract between the landlord and A, B & C (jointly and severally) which is a legally binding contract [the lease] and the other is the agreement between A, B & C which might be (but probably isn't) a legally binding contract [the roommate agreement].

If C can sublease and to whom and in what circumstances depends first on the lease - it is quite comment to have a no subletting clause or to be able to sublet only with the landlord's agreement.

Only if the lease allows subletting do we turn to the roommate agreement. Unless you have actually written this up and agreed that it will be a contract between the three of you it probably isn't one and isn't binding on anyone. If you don't have a binding agreement and the lease allows C to sublet, neither A nor B has any ability to restrict who C sublets to.

Further, barring a binding roommate agreement that allows it, no tenant can force any of the other tenants to move out.

First, you need to understand that there are 2 agreements here: one is the contract between the landlord and A, B & C (jointly and severally) which is a legally binding contract [the lease] and the other is the agreement between A, B & C which might be (but probably isn't) a legally binding contract [the roommate agreement].

If C can sublease and to whom and in what circumstances depends first on the lease - it is quite common to have a no subletting clause or to be able to sublet only with the landlord's agreement.

Only if the lease allows subletting do we turn to the roommate agreement. Unless you have actually written this up and agreed that it will be a contract between the three of you it probably isn't one and isn't binding on anyone. If you don't have a binding agreement and the lease allows C to sublet, neither A nor B has any ability to restrict who C sublets to.

Further, barring a binding roommate agreement that allows it, no tenant can force any of the other tenants to move out.