My common-law husbands house, where we now reside, is willed to his three grown children. If my husband should die before me will I have to move out of the house right away or does the law grant me some time?

First, Any question on law needs to include your general locale as laws vary by area. Most areas do not recognize common law marriages. So the likelihood is you will have to leave. But it will take some time for the will to be probated before they can serve you with an eviction order. They will have to give you at least a 30 day notice to vacate.

This is something you should talk with him about openly, especially if you are not a legal wife. He can send a notarized statement to each child and you, stipulating that you get to live there X amount of time after his death, even if it's for sale. Have it specify who pays property taxes and utilities and repairs and insurance. If you will have nothing but Social Security, you should look into the wait time for senior housing. And so on - get your ducks in a row.