tools
dont know what these fasteners are or how to remove them. Some kind of bolt i think.
Bolt head is totally smooth and round. Screws into a circular receptical with a tiny circular divit. Can't figure out what tool could get any traction on either the head or the receptical.
Ratchets can be rather bulky as you've found. Combined with a deep socket in the wrong place, you aren't going to remove the fastener. Using a shallow socket and and proper length extension moves the ratchet out of the way to where it belongs.
Straight Drive Extension
Wobble Drive Extension
The wobble drive allows for some misalignment between what the socket is removing and the ratchet drive handle, probably what you're looking for to take care of the fact that gear is in the way.
Or you use this drive handle to convert the socket to a simple nut driver
Then there's the time honored nut driver
I'd go for my pull saw or my oscillating saw/multitool
You should be able to get most of the way through with the oscillating saw and then finish it by hand with a compact hand saw. I like my compact pull saws to tight spaces like that.
Best Answer
It's a rivet. You can drill it out with a metal twist drill, countersink, or countersink deburring bit.