My ex-wife died last week, do I now get custody of my two minor children?

I am sorry for your loss.

I am going to assume that your ex-wife was the custodial parent of your children and that you had visitation based upon a custody agreement between you.  I am also assuming that your rights to your children were not terminated in any way (voluntarily or involuntarily) or that their step-father did not adopt them.

You now need to do things and I would strongly suggest that you hire an attorney in your area to assist you: you need to go to court to establish you as the legal guardian of your children (you are the natural guardian but you need the court behind you legally) and you need to modify the prior order of custody. You child custody agreement survives the divorce and should list in it the court that retains "jurisdiction" - the right to hear matters that pertain to the children. Do this quickly and good luck.