Attach CharacterA hand bone to CharacterB hand bone

How can I attach the hand bone of one character on to the hand bone of another character(such that they are holding hands)? Both characters are playing idle animations that are not perfectly sync’ed therefore the bones have to be attached to one another or position of one needs to update per frame its position to match the others.

Currently in my setup, character A approaches character B and moves into a position that character B dissapears then a mesh becomes visible in its place that is parented to character A so that they move together, this creates the illusion that A is holding B which is great, problem is the idle animations are not perfectly synced and so as A breaths in B breaths out and there is some noticeable clipping etc. If A hand bone could be attached to B then their bodies can be non-synced and the hand would maintain position on the other character while other animations do their thing, similar to how real life holding hands would function.

I have been working on this for months and cant figure it out. I am weak with IK and it so far hasnt produced the results I need anyway. If anyone can help me with this I would be extremely greatful.

There is little to no help that I can find with this issue of attaching character ‘A’ bone to character ‘B’ bone.