Bats and damp in an OLD stone property

Looking at a house/barn that was built in mid 1600's and re-done in 1990. Two issues that I thought I'd hit you with in one go....if I get a damp bat expert I'm sorted!

So - they have bats.....like...a lot - owner estimated 300+ roost in one part of the attic. I have no problem with that as I hate mosquitoes more than bats! However, there are a few outbuildings that I would be looking to flatten or replace and a few trees in their wooded area that might need thinning out...... If you have a property with bats, does the protection of them extend to making changes to their "hunting ground" - my garden! Or if there is an old falling down stable block that I don't want, I can just demolish it without a second thought?

And the property has one original wall that had no signs of damp for a few hundred years, and when the current owner brought the whole project up-to-date in 1990 he was forced by planning to inject damp proof into the stonework. And suddenly the wall got damp and the company that did the work went bust. As such, he has simply got one slightly damp wall that he ignores - it's hidden behind an old fireplace that is no longer in use at the back of the kitchen – so no big deal for them.

Is that a- likely to be fixable with upgraded ventilation, etc in the rest of the house. b- no big deal, and you didn't bother them it shouldn't bother us and c- to be a dealbreaker for my mortgage company! Everything I have read on injectable DPC makes it sound like the whole thing was a bit bit of a scam – but no one explains how to fix a failed wall that had it done.