First, manasshkatz correctly spotted the alien breaker second from bottom on the right side. The lower left breaker is a Siemens QP. Those alien breakers have gotta go. You need "Westinghouse" (read: Cutler Hammer/Eaton) BR/C family, commonly known as BR.
The 30A Siemens is a mystery. There's almost no legitimate use for a 30A 1-pole breaker. I accidentally bought some of those, and they have no application I've found except for small travel trailers with a TT30 plug.
So it looks like someone oversized a breaker for the wire. The two 20A breakers above also look highly suspicious, since those and the 15A breaker above it all have the same wire size. I'll bet those are 12 AWG aluminum wire, which is only good for 15A. I'll bet the 30A breaker is #10 aluminum, only good for 20A.
Other than that, I'm not worried about aluminum wire in this panel. Aluminum belongs here. The branch outlets not being CO-ALR rated, that's the issue with aluminum.
Also, I see where all the wire entries are via conduit, and there's Romex cable in the conduit. It is fine to use conduit solely as an anti-damage shield for some segment of the cable's run, and in such application you can disregard the conduit-fill rules. However, if the conduit is the entire length, then it's not just a damage shield; you're running in conduit and the fill rules apply. Cable in conduit wastes space in the conduit, and is usually an illegal overfill - oval cable counts as a round wire of the wider dimension, so e.g. a 12/2 Romex will overfill a 1/2" conduit because a round wire of its width would not be allowed. You can get much better use of the conduit using individual, unjacketed THHN wires, Sched 80 PVC will support 3 circuits, other sizes 4.
Also, I would recommend obtaining accessory ground bars and splitting the grounds. That way conversion will be simplicity itself.
2-pole GFCI breakers
GFCI devices have very little concern for what safety ground is doing. They do not connect to safety ground in any way, shape or form. Even the GFCI "receptacles" do not connect to safety ground at all. -- except it's wired to the third prong on the sockets obviously.
So your 2-pole GFCI will be "gliding above all" the grounding issues in the panel. It simply doesn't care.
You also might want to think about AFCI breakers to protect the aluminum wire 15-30A branch circuits. That's the easiest way to take a bunch of risks off the table.