complete novice needs help, probate?

What is the name of your state? California
I am a total novice, so please excuse my ignorance! My mother died 6 months ago with a will. Her only asset was a 1/4 interest in a 130+ acre unproductive agricultural land where she lived in an old farm house. She got sole title to it when my father died and left it to his surviving spouse (no probate required)... her interest was left to me and my 2 siblings. The other 3/4 owners want to lease a portion of the land and need us to sign off, but the deed is still in Mom's name. What do we need to do to get on the deed? I guess we should've dealt with this sooner, but**************************** What is the name of your state?

You need to open a probate estate.

Preferably no later than 30 days after ma died.

Is the realty worth over 400k for 100%? If not, look at Probate Code Section 13150 before you open a probate.