Thank you for following up with me.
As a legal guardian of your son who is a minor you are legally entitled to pursue a claim of his in law in Texas.
You can get a copy of the will when it is filed with the County probate court where grandfather died. This will be a starting point.
As far as your son's entitlements to challenge the will. Texas probate law allows an interested party to file a will challenge to challenge the will and its validity.
This would be in your son's interests from what you have described. Your son qualifies as a person that can challenge a will, because he stood to inherit but for the will that seems to be out of character for your grandfather.
You can challenge the will on his behalf: either under undue influence from the people you have described
(2) lack of capacity of the grandfather because of his illness, you indicated he was sick when he made the will changes.
Probating a will can take up to a year but should be available to inspect after a few months. The usual time to probate a will is about 4 months, so you should file any will challenge within this time.
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