1. IF a Contract (agreement) has been signed by two persons jointly (B & C on one side), THEN by default both the persons are liable jointly and severally, to the other side (A).
2. Lawfully, there is no need to "expressly state parties B and C are jointly and severally liable to A". However "IF" the said Contract specifically & written'ly states (vide a specific clause) that only "B" shall be responsible for the liability to "A", THEN ONLY due to this specific clause, the liability of "C" is absolved.
Keep Smiling .... Hemant Agarwal