How can I get a copy of my mother-in-laws Will?

Are you listed as a beneficiary? Is your wife? As a matter of law, all people receiving a bequest (gift) under the terms of the Will are notified. At that point you have a right top see a copy. If you are not mentioned in it, then you have no right to see it. That is until it is entered into probate. At that time it becomes a matter of public record and anyone can obtain a copy for a small fee.

Note:  If you mother-in-law is still alive, then without her permission you have no legal status to see a copy of her Will; she would have to give her consent.