You might want to use one of those blue wash out fabric markers to mark 1/2" inside the borders of your block and ask everyone to please stay within the markings. That way if they go just a hair over it won't hurt.
With using permanent pens for signatures you don't have to embroider over them unless you just want to for a more authentic look. Personally if there are people that are deceased that you want on there I'd do all those myself and print their names. That would indicate that at the time the quilt was made they had passed on. You might even want to put birth and death years on there.