setting MR clock to internal
Yes that has to happen - since your Apollo doesn’t have ADAT or WordClock output. So in your setup the MR definitely has to be the clock master device.
However you may want to set your Apollo Twin clock to ADAT, so that the MR and the Apollo Twin are synchronized properly and you don’t end up with weird audio artifacts from time to time.
p.s. I’ve read somewhere that it can seemingly work to have both devices use their internal clock, but that it risks bad audio artifacts (probably just when you are recording your best take ever!) 