Spanner or socket & ratchet.
Tried a spanner they won't budge thinking about using a holesaw just to cut the wood off and then as a last resort cut the bolts
Stick a pole on the end of your spanner to give it some extra leverage, a metal pole not an Eastern European. Or even an extra spanner:
I presume they have rusted under the surface and seized into the substrate. What do they screw into? Are they coach screws?
If you have a blowtorch with a fine pencil flame, you can heat the head, and it will probably crumble the rust or scorch the wood enough to unscrew. If plasplugs, they will melt. Protect the timber with a piece of metal or tile with a hole just big enough for the head.
But I had some galvanised studding into RC fenceposts rusted so badly that I had to drill them out. I drilled the heads off and used a fine drill beside the studs.
I use stainless bolts now, and big stainless washers.
If you have a blowtorch with a fine pencil flame, you can heat the head, and it will probably crumble the rust or scorch the wood enough to unscrew. If plasplugs, they will melt. Protect the timber with a piece of metal or tile with a hole just big enough for the head.
But I had some galvanised studding into RC fenceposts rusted so badly that I had to drill them out. I drilled the heads off and used a fine drill beside the studs.
I use stainless bolts now, and big stainless washers.
Not to sure but there 3 bolts in total all look like there sat in the middle of bricks. I'd like to reuse the holes as don't fancy drilling into the brick and risk it cracking.