Sorry, Phil, I realised there are a couple of angles that may be applicable that I hadn't addressed yet, which are undue influence and suspicious circumstances.
'Undue influence' is quite difficult to establish, and the onus to prove is on the party alleging it, ie you. You have to establish that the deceased didn't really want to leave everything to the young couple, but that they pressured her to do so. If she had time alone with the solicitor during the preparation of the will, and the solicitor preparing the will didn't feel that she was being coerced, this is going to be extremely hard to establish in the absence of something extreme such as recorded threats.
The other angle, perhaps more applicable, is 'suspicious circumstances'. If the solicitor was friendly with the beneficiaries, and was not previously your mother's solicitor (unclear to me - you refer to the solicitor as 'her solicitor'), and the new will disinherits people who were previously significant beneficiaries, that probably meets the definition of 'suspicious circumstances'. Once suspicious circumstances are demonstrated, the onus of proof reverts to the beneficiary of the suspicious circumstances to demonstrate that the gift was made freely as a result of your aunt's wishes, and not due to the suspicious circumstances. If this can't be proved, then the clause benefiting that party is usually invalidated.
This is not specific legal advice, obviously, because I don't know all the facts, but may give you an idea what questions to ask your solicitor.
'Undue influence' is quite difficult to establish, and the onus to prove is on the party alleging it, ie you. You have to establish that the deceased didn't really want to leave everything to the young couple, but that they pressured her to do so. If she had time alone with the solicitor during the preparation of the will, and the solicitor preparing the will didn't feel that she was being coerced, this is going to be extremely hard to establish in the absence of something extreme such as recorded threats.
The other angle, perhaps more applicable, is 'suspicious circumstances'. If the solicitor was friendly with the beneficiaries, and was not previously your mother's solicitor (unclear to me - you refer to the solicitor as 'her solicitor'), and the new will disinherits people who were previously significant beneficiaries, that probably meets the definition of 'suspicious circumstances'. Once suspicious circumstances are demonstrated, the onus of proof reverts to the beneficiary of the suspicious circumstances to demonstrate that the gift was made freely as a result of your aunt's wishes, and not due to the suspicious circumstances. If this can't be proved, then the clause benefiting that party is usually invalidated.
This is not specific legal advice, obviously, because I don't know all the facts, but may give you an idea what questions to ask your solicitor.