Hi,

If they look the same from both sides you can attack the rivets with a small rotating wheel
taking the tops off, the big from the rear the small from the front, in doing do you might
damage the the middle fixed ring, but that doesn't seem to matter in this case.

Looks like get the small off first and then the big. Hire the tool if you don't have it.

If you don't want to hire tools, centre punch and use a big enough drill you can tell
the flange of the rivet has separate from the rivet. Again as long as you don't mind
trashing the fixed middle chain wheel, no great accuracy or finesse is required at all,
drill it through to just the centre chain wheel and then punch out the rivets.
(TBH is actually very hard to trash the centre ring stopping at the obvious point).
Attack the small from the front, then the big from the rear.

Both recovered chain wheels will be undamaged.

rgds, sreten.