
Basically, one of them is not tight, but it's seized so I can't tighten nor loosen it. The other one is also not tight enough, and while not seized, I can't get the stupid little spanner thing to stay in those grooves:

I was having all sorts of issues with my gears when I was away last week, and when I got back, I found the plate was so loose I'm surprised the bolts hadn't fallen out. I'm now worried it's damaging the mounting points on the frame, so intend to drill out the seized bolt. I just don't know what these things are called, so not sure where to get replacements from...?
Is it possible to get a variant that is hex keyed on both nut and bolt halves...?
TIA.