The basic position is that you cannot change the way you hold your interests back to joint tenants unilaterally, you would need the consent of your husband to do this. There is nothing that you can do about it now to rejoin the tenancy to a joint tenancy I'm afraid. That is a persons right.
His interest would pass according to his Will. If you suspect that your husband has made and executed his Will under duress from his son, or that he lacks the capacity to do so then you should speak directly to your solicitor about this.
A person can make a claim if they are not provided for in a persons will after death if they can show that they were wholly or mainly financially dependent upon the deceased prior to death under the Inheritance (Provision for Family and Dependent) Act 1976. This would require an application to Court to be made within 6 months of the date of the grant of probate, it is fairly costly in legal fees as well. If you have a solicitor who is familiar with your specific position in this regard, but if your husband has made provision for you to an extent then your prospect of success in this application is decreased I'm afraid.
A further matter to consider is that if you have in fact contributed more to the financing of the property then you could consider asking your husband to execute a declaration of trust stating that you own a greater percentage of the equity in the property than he.
Sorry it could not be better news.
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