I've just realised after typing my second paragraph above that the easiest (meanest?) most obvious way the FIL may have chosen to exclude the OP and her son (the grandson) is if:
● the FIL changed his Will to simply gift his Estate to his own direct line surviving children (with no provision for what happens to the share of a deceased child).
● if the FIL had done that in the last year or two of his life, he could have cut grandchildren out if his Will entirely (and removed Trust provisions for the grandchildren) and left lump sums to his surviving children for them to deal with or distribute as they see fit
(ie. if those adult children decide to share part of the inheritance they receive with their children - the grandchildren of FIL - then that becomes a private matter and personal choice for them).
This scenario is, unfortunately, the most likely explanation of why the OP has not heard anything.
But also a good reason for the OP to try and establish the facts, obtain a copy of the Will (from the 3 places it may be possible to obtain a copy).
And whilst it would be sad and disheartening to know that the FIL had actually deliberately excluded that grandchild -- it would provide clarity.
The issue for the OP at the moment is that she just does not know what the situation is either:
(a) FIL did change his Will;
(b) the Executor is being slow and uncooperative but there is a provision for the grandson but OP has not been informed;
(c) the Executor is actually acting fraudulently keeping everything for themselves and not informing people and not performing their Executor duties correctly.
Which is why the first step for OP is to try and obtain a copy of the Will to establish what the actual situation is.