jack point problem

[Roderick]

Hi all. An increasingly familiar problem I believe after doing some searches on here.
I was looking near the rear offside sill and took some photos of where the rubber jack point is. There is evidence of rust but also some crack openings. What’s the current advice for making the best repair possible barring eventual replacement and welding?
I have an anti rust treatment called Ferox which has proved pretty good but it’s surface stuff only.

There are only 3 jack points fitted, the front offside is missing. I know some say take them off. Well I tried, but after 17years, it’s well and truly stuck. How are they supposed to come off?
Sorry photos are not good but hopefully show the problem.
Thanks, Ray.