Selene would only ever use her magic speed buff on her own, never the other one and she never uses Silence on her own on Obey. So you could really just leave her on obey and use the melee speed buff when the magic one expired. It was extremely simple with her.

Eos you would just leave on steady and use WD whenever you thought you needed. With a WHM in the party I personally never needed to in HM primals so I would usually use Selene instead.