yes you connect the way you say and The focusrite’s will clock via ADAT. you can daisy chain the fire wire connection on the two MR units so you’d have 32 IO with your 2 focusrite’s.
Be aware though that you’ll only have zero latency direct hardware monitoring on your first(master MR unit) so in your case that would be the 8 MR analogue inputs and the 8 focusrite inputs connected to it via ADAT.
MC