Tread Replacement

Hi all, amateur but reasonably capable home handyman here with a question.

The previous owners of this place weren't up on their maintenance and the hardwood treads on my stairs have been let go. I've got new hardwood treads ready to go, however. I can't for the life of me figure out an order of operations.
I've got four sets of stairs off my decks, 2 are just open riser / closed stringers. But the one that needs replacing is an open riser, closed stringer. But it also has a sawtooth stringer for support in the center, as they're 2.2m wide.

All three are notched and are sitting over the bearer.

So I can't knock the treads out backwards because the center stringers in the way.

Looks like my options are either... Detach the entire staircase from the house (Looks like the stringers are only held in place by a single nail. Jack it / Acro it away from the house enough to drop the center stringer.
Knock out the treads and replace them with new. Drop it back down reading on the bearer again. Nail/screw back in and walk away.

The other option is I just replace my center stringer with a steel one, but this doesn't allow me to replace the top step tread still as I'd have no access to knock it in from behind without the bearer being in the way.

So it looks like I've got a bit more work ahead of me than I thought?