If you turn off RCS a day or two before switching and ensure you message these groups after this is typically negated (at least in my experience) GrapheneOS just put out a way to use RCS on its OS this month which is really nice, I have it on its own profile for RCS and use open bubbles for iMessage/FaceTime and I'm astounded how well it works tbh. But the goal is to slowly harass enough of my frequent contacts to get on signal, so far I'm doing great, my largest hold out being my wife lol