>>> However he has to go the Solicitors on Monday
Unless they're in the army, under arrest or on their way to prison (etc), nobody ever has to go anywhere. So he must have received an invitation to attend the solicitor's office and it seems very odd that the invitation didn't at least give a hint as to why he should want to do so!
The first thing that happens when someone dies (in relation to inheritances) is that the executor(s) need to get hold of the will. They'll then need to collect together all of the necessary information in order to apply for probate.
Since it would seem to be highly unlikely that probate has already been granted (given the short timespan), the executor(s) of the will must still be at the 'information gathering' stage.
Indeed, it's possible that the executors (if more than one executor was named in the will) have yet to meet to discuss the way forward. If, say, the will named the solicitor and the two siblings as joint executors, then the solicitor would obviously need to speak to the other two people involved.
Similarly, if the will was only held by the solicitor (without him/her actually being an executor) but named the two siblings as executors, then the solicitor would need to ensure that they were both aware of their duties (while probably dropping very broad hints that they could pay him to do the job for them!)