Are these parts reusable?

do these look ok?

Difficult to tell from the pics. Could try to re-use the MC piston and primary cup, if neither cup is torn or cracked or obviously damaged, the main thing being that it doesn't leak out at the lever end.
One thing to watch for is pitting inside the MC bore, which if not too deep may be dressed/smoothed to a serviceable condition.

The caliper piston may also be restored to serviceable condition, provided it doesn't allow fluid to escape toward the pads.

While disassembled, would recommend obtaining MC kits and a Caliper kit, to do a first class resto job, as brakes are [you know].

The CS sprocket is beginning to "cup" and is a relatively inexpensive replacement item. Before returning the bike to regular service, would replace both sprockets and the chain.

Z1 Enterprises is a good source for all these parts.

Good Fortune!