Pete,
Please don't be put off from having a go by my step-by-step guide.
I merely try to give advice as I would like it given to me, that means a bit OTT on the detail but covering any possible problems.
Looking at the overall condition of your car it would surprise me if you had any dramas removing the liners. The probs with the hex screws come from the car being driven on British winter gritted roads, it doesn't look like your aunt took her car out in these conditions so the fittings should be fairly well preserved...likewise for the bumper end bolts.
Have a good look at each liner on both sides and see what condition it looks in, if you think you can tackle the task have a go, if not, get someone mechanically experienced to have a look for you.
Maybe take some pics and post them on here......then everyone can have a look and possibly give you better advice?
.?