Your difficulty is that, as a purchaser, you should make your own enquiries. The vendors solicitor is going on the basis of the info supplied by their client. Your solicitor has passed on your queries to the vendor's solicitor. But it is for the vendor to choose how to deal with those queries - their solicitor can only act on their instructions - vendor's solicitor does not themselves carry out an inspection of the property.
My advice? Spend the money on your own Architect/Engineer and let the two experts battle it out.
The old adage of "the day you buy is the day you sell" is imperative. All the leverage is before contracts are signed so get it sorted now, establish the nature of the issues and how they should be dealt with/resolved before contract and what risks, if any, you are willing to take.
Do not rely on suing someone else's expert. It could be a long, expensive and futile exercise.
mf