I'd dig up the perennials and extract all celandine roots from their root balls, and dig around the area I lifted them from and replant the perennials, watering thoroughly. As for the celandine amongst the bulbs, wait till 6 weeks after the bulbs have finished, then repeat the procedure as for the perennials.

Young creeping buttercups are often still connected by runners to the mother plant, so loosening the soil around them sometimes means you can get more than one at a time. It is possible to pull them out from among perennials if you lift the perennial slightly and grab the buttercup as low down as you can. It usually entails shoving your fingers down into the soil to get a good purchase on it. As long as you get the growing point out they won't regrow - unlike dandelions!
It calls for patience as you have to do it with a hand trowel. Any that you simply can't get at can be killed by painting the leaves with glyphosate, rather than spraying them. Its important to get them all out though, as each plant left in will produce lots more in short order! If your bulbs are very close together maybe one of those very narrow trowels would help. Otherwise wait until the leaves have died down, but in the meantime remove any runners so they don't spread any further.