If Ember's feeds and Raven's meal times are clashing, why doesn't she make food for Raven in advance and bung it in the fridge for later? Like a packed lunch.
I used to do it for myself when mine was a baby and my Husband was working, because he used to cluster feed right through teatime.
Either that or tell the child that is old enough to understand, that she may have to wait a little while, because the child that can't understand needs a bit of attention first.