Well, if it is just for guardianship then you can literally just write a blog post and then send certified letters to everyone you know telling them the order of people you would want to care for your children. Judges don't actually want to have to decide who gets the kids, they will actually do what is easiest and if 30 members of the family say "oh, Jack and Jane wrote us a certified letter that says they want Mary and Bob to raise the kids and if they don't want to do it then they want Alice and Jim to raise them..." then the judge will go with that.
Now I am going to tell you not to write a will, I am going to tell you to write a trust! When you die, the money can not go to your children if they are minors and if you have them as the beneficiary then the money will be held for them until they are 18 and then they get a lump sum (and what things would do if you got about a million dollars at 18? something stupid or college?). This means that the people caring for your children will not get any help monetarily to raise your children. If this doesn't happen then the guardians will have full reign over that money and can do something stupid with it, like pay off all the credit debt they have! With a trust, you can have a bank pay the people caring for your children a set sum each month, or pay for private school, or whatever so they can raise your children in a comfortable way. You can also say something like you want the kids to visit each set of Grandparent for at least 14 days each year or they money will stop (not that you would).
My mother is a lawyer in trusts and wills, she has seen so many abuses from care givers when it comes to money. Cases like the aunt (dad's sister) and uncle that got the children, used the money for IVF, got quads, and then handed the now penniless kids over to the maternal grandmother living on her SS check. They tried to sue the aunt and uncle for the money but aunt and uncle didn't do anything illegal and as such my mom couldn't help them at all. The kids ended up in Foster Care because grandma couldn't keep the kids and the house and after grandma lost the house, well, CPS took the kids.