Father's Will leaves his mother his estate. He is living. She is deceased. I am his only heir; would I inheirit his estate--would her other children?

No one can tell you exactly what would happen to your father's estate if he dies with the Will you describe still in effect without seeing the Will, because a lot depends on what, if anything, the Will says happens if his mother does not survive him. If the Will provides for an alternative beneficiary or beneficiaries, then that's what will likely happen. If the Will really doesn't state what should happen to your father's estate if his mother, the primary beneficiary, does not survive him, then he may be deemed to have died without a valid Will in place, and then his estate would go to his hers, not to his siblilngs. You're right: your father needs to get his estate planning updated as soon as possible, to ensure that what happens at his death is what he WANTS to have happen. Your are wrong to tell him to write out his wishes and have them notarized as a stopgap measure: that would not have any legal effect. In the meantime, he needs to have the Will reviewed to see what it provides in case his mother does not survive him. If it provides for a distribution that he does not want to have happen, if you are really likely to be his only heir, and if he really wants you to receive all of his remaining estate at his death, then he may actually be better off revoking the existing Will until he can get the new one in place. However, if the existing Will actually makes an alternative provision that he's happy with, he can likely leave it in effect until he's gotten the new one prepared.