1, it depends on who needs it. If it is external, such as Party A, then no matter who is the first responsible person, if there is a breach of contract, the signatory parties shall bear the corresponding legal responsibilities according to the agreement. If it is internal, an agreement can be signed to stipulate the distribution of responsibilities between two people. This agreement is legal and valid.

Be cautious about the contract. The clearer and more detailed the regulations, the less likely it is to cause disputes. If both parties agree to a supplementary agreement, it is ok to sign another one.

If there is no division of labor among the first responsible person, the second responsible person and other second responsible persons in the terms of the contract, there is an agreement on the responsibilities of Party B, or if necessary, the responsible person of Party B shall sign it separately. (It has nothing to do with Party A. In case of contract dispute, Party A may require all responsible persons of Party B to bear the share, and all responsible persons of Party B shall bear the share as agreed).