Why won't my kids trust the advisors my dad has used for thirty years?

Because the advisors are perceived as the founder's guy, not the family's. Long-term advisors build their relationship with the founder generation. The kids watched it grow up around them. Even when the advisor tries to be neutral, the kids see someone whose loyalty was earned by their parents, paid for by their parents, and shaped over decades around their parents' priorities. Kris Kluver, in The Dysfunctional Family Office, has Robert Mitchell recognize this about his own banker. He likes him. He trusts him. He also acknowledges the kids will see Brian as Dad's guy. The fix is to build new advisor relationships earlier than feels necessary, with the next generation actively involved in choosing them. Or to bring in a facilitator the family chooses together.