Something to consider here is the fact that Dain is portrayed as being very considerate and forgiving. So this slight is most likely something that occurred accidentally or unconsciously. Perhaps it didn't happen at all...1) family still in the Iron Hills, but the clan elder hates Dain for some childhood slight - the party need to learn the cause and heal the rift
A dozen dwarves at a gathering are displaying examples of their crafting ability. One participant scratches the work of the Elder and Dain sees this occur. He tries to convince the guilty party to own up, but he refuses. Worried he will be revealed, the guilty party blames Dain, igniting an argument amongst the group as members take sides. Dain never reveals the guilty party, but this life-altering event is a part of the reason that Dain is forgiving. He knows that greed and animosity only leads to trouble.
Something to prevent simply replacing the noble families is that each line has a crafted ingredient that is needed to re-ignite the Forge. No single family knows all of the formulas. Each knows the formula for a single catalyst - which are useless without all of them present. The Ritual is really just a ceremony which allows a bit of sleight-of-hand so that the families can introduce their ingredient into the Forge without revealing the secret.
This would change the 4th option slightly, requiring that a written record of the formula be available. It could be hidden in a secret compartment or lying out in plain sight in the family library.