Personally, I'd go for #3. CC-BY is just one small step up from PD, so I really don't see the practical harm.
Wiki Commons is used for a lot of things. Copyfraud promotion should not be one of them.
I explicitly advise against using #3 for this collection or any other. Using #3 would imply that we a) didn't care about the public domain and b) didn't understand the idea behind CC licences.
If we acknowledge such copyright claims, we also acknowledge the possibility of legal action in case of copyright violations (e.g. by violating the terms of the licence).
Apart from this ideological thought, the actual legal enforceability of these copyright claims depends on your local jurisdiction.
Yet, I don't think the Wellcome Library released this collection with the intention of pursuing licence breaches.
It's not like we didn't encounter this issue before.
Regards, Christoph