You can put whatever you want in your will, and nobody can stop you, but I assume you're asking if such a provision in a will would be binding. But to answer your question, yes, in your will, you can nominate someone to become the designated guardian of your minor children, and this will be given considerable weight by the court. Of course, when a court is deciding child custody matters, it will always consider the best interests of the child first. I have no idea what your personal situation is, but if a court decides that the children would be better off with their grandparents (and the grandparents are seeking custody of them), the court could conceivably ignore the will, and grant custody to the grandparents. However, if it is convinced that your brother and his wife would be good guardians, it will probably defer to your wishes. This should go without saying, but make sure you discuss this with your brother and his wife, to ensure that they're willing and able to take custody of your children in case something happens to you. Here is some basic information on estate planning, and some things you should think about when making an estate plan: http://www.legalmatch.com/law-library/article/estate-planning.html