This is what I would do. You say the colony is three years old and healthy. Your parents have waited three yrs already to use the fireplace.
I would hold off on removing them but place at least three swarm traps out, maybe one 50', 100' and say 200' from the house.
A healthy hive like this will throw off at least a few swarms every year. Catch some swarms and you will have some of their genetics.
A chimney removal is a tricky one, no guarentees you will get the queen, hopefully you will get brood comb with eggs and young larvae, but what if you don't?
I say catch some swarms, set them up, and then do the removal. That way if you just get bees and no queen or usable brood, you still have the genetics and you could combine the bees with the other colonies.