Nothing at all to stop you. Might be best not to name them as executors. It’s a myth that you need solicitors to deal with wills; you don’t. It can help if you’ve got complicated legacies, and there will need to be some legal involvement if there’s a property to sell, but wills can be drawn up by anyone. Also anyone can be a an executor; I’ve done a couple of family wills, and they are quite easy, it’s just the fear of the unknown that is offputting.
Just remember a witness cannot be a beneficiary. Make sure you store it safely, and that it’s whereabouts is obvious – both yourself and SWMBO could be involved in a car accident, so relative strangers will have to go through your papers, if they can find them!