Will a hand-written account of our wishes hold up in court in the event of our death?

It seems the legal fees to have a will and trust drawn up by an attorney is a little over $2k. We (my husband and I) have two small children and we’re very particular about who would get custody of them if we were to both die. Since this would change every 10 years or so (or more often depending on their changing life circumstances) depending on their age, we don’t want to pay to have new wills drawn up so many times. Would a hand written, notarized letter that detailed our wishes hold up in court? The person we wish to have custody is a family member but not a grandparent. Also, we have particular people that we want to get some of our assets. Our life insurance policies are written correctly, but I’m talking about our kids and our cash and other assets. Everyone involved knows our wishes and we have a verbal agreement that they would see our wishes were met. We get along well with all of our family and really have no reason at all to believe that anyone would sue or fight against our wishes. If it matters, I live in Mississippi. THanks!!!