Agree with Am. when A retired it should have all been sorted at that time. What B and C arrange between themselves, now that A has retired is nothing to with A.

From what I understand B and A had an agreement, Party B and C had an agreement, and Party A and C had an agreement. This is way to complex and it needs to be dealt with. They need to go to Party A (now retired) and seek that any agreement with them is nul and void as at the date of retirement. So then only photos taken before that date are bound by those agreements. Then party B and C need to get together and arrange new agreements that suits them as they move forward.

Party A's involvement at this time should only be with photos taken before they retired.

Copyright depends on what each of these agreements has in it. It is not as simple as it not being domestic portraiture, as any agreements probably have ownership written into them. However, it also seems that there could exist a real conflict between all these agreements at present where so many different copyright ownership issues exist that one agreement might just negate out another.

Considering Party A's retirement, they need to:

Contact Party A and cancel that agreement as at date of retirement.
Work out what happens to photos taken under that agreement (ie prior to retirement) and get a new agreement regarding those
Then Party B and C need to create a new agreement that does not include Party A at all.

It all just needs simplifying.