The solicitor will have Professional Indemnity Insurance, so if they have screwed up it will be their insurers paying out. If it is a clear cut case they will be keen to settle and move on, so be sure of what you want from the claim.
The vendors will be more difficult as they are unlikely to have insurance so will be stumping up from there own money - hence they are likely to battle to the last rather than roll over and pay (unless they are cash rich).
See if you have any legal expenses insurance (bank accounts, credit cards, FSB membership, Union Memberships and your Home/ Car Insurance all may have this feature as a bolt on extra - if you have consult another solicitor and set the hares running. Your original solicitor will not like a potential complaint letter from your new solicitor and will have to put their insurers in notice of a potential claim if they have not done so already.
This is not legal advice in any way, it is just what I did when I bought some commercial premises a few years ago and the solicitors screwed up, we received compensation that ran into tens of thousands because of their error. As a warning, even on a relatively straightforward case (the solicitor admitted liability almost immediately)the settlement took over a year. The insurers viewed liability as the first issue and then negotiated over 'Quantum' - how much we had lost financially for quite some time.