I think you have several lines here but to answer your latter questions first, any information that your son was given by your late husband would not necessarily be privileged and it is often the case that information is passed on to a solicitor for use in a court case. The use of a council email system for personal use may be in breach of the council's email policy and you may have cause for complaint there but again that won't help the bigger picture. What is the case is that you can establish that the funds were originally held and owned jointly and that your husband "stole" the funds into his own account. After he died you made a claim on the estate and the money was returned to you. The children would have to sue the estate and I don't think they would win. In any event as there was no will you would be entitled to widow's prior rights of £50000 and legal rights of a further third of the remainder. I oresume this was taken into account? Happy to discuss further.
As the account was joint it would be looked on as joint property and you would be entitled to half. The fact that he had more money or that you didn't work isn't necessarily relevant as you would have looked after him and the household. You could take action but it's not the type of case that a solicitor would take on a no win no fee basis as such actions are unpredictable. However there's no reason why you couldn't see a no win no fee lawyer for an initial consultation to see what they say. I hope that helps. Please leave a positive rating so that I am credited for my time.