What you are speaking of is instituting a Will Contest. The basis of most such contests are either the Deceased wasn''t of sound and disposing mind when they had their Will drafted for them. Second, if the Executor is trying to hide a second Will that changed anything and post dated the first Will that is being offered to the Surrogate's or Probate Court. Or the Will wasn't properly executed.
If they Executor is "trying to hide assets" then that could be a basis for seeking to have the Executor lose their position in the proceedings. However, if you are making such a claim, you must prove the claim.
If you sue the Executor, usually the Estate pays their fees, unless you eventually prove that they are actually doing something illegal or improper or not in the best interests of the Estate. You must pay your own attonreys fees if you institute such an action, unless you are proven right and the Court awards you attorneys fees because you were doing something beneficial for the Estate. Each state may have their own laws, so check this out with a local attorney as well.