...then i also need to see what you're using for the wrench. I think there's a flat one and maybe a sort of cupped one, too for that design.

If it's the flat one, you get some large washers with a hole that will clear the crank spindle end, and use at least one big flat fender washer
to go up against the wrench to hold it in place, fill in the rest of the gap with the other washers (or you can make a spacer out of a small piece of pvc),
and then use your crank bolt and another combination of washers (stepped down in hole size) to hold the whole thing together.

The attachment should be tight enough to hold the wrench in place, even when you hit it with a hammer, but still a little loose so it has room to back out a turn.

I think I'd try the loose cup (the one that slides off the cartridge) first. Once that one is loose, you still have a spindle to attach to on the other side.


If the cups are aluminum alloy, I'd try degreasing and then trying to get some ammonia in there for a day or two (you can pour it in through the seat tube.)
Then apply some sort of penetrant oil, and attempt the procedure as described.

Bolting the cup wrench in place so you can hit it with a hammer seems to work like a primitive impact wrench.