Don't worry. K+ and Na+ will not react with each other. In fact, I don't think they'll react with just about anything. They are used in many chemistry experiments where a non reactive ion is necessary. In fact, the only way I know of to even precipitate them (bring out of solution) is to either electrolyse them, a process that requires large, expensive, specially made equipment (to simultaneously melt pure KOH or NaOH, run a large current through it, all while keeping it out of contact with either air or water), or to add some sort of bizarre Uranium salt.
Remember, K and Na are alkali metals. Of all the metals known to man, they are pretty much the most reactive (most of us here have seen a video of sodium exploding in water). Conversely, since the unreacted form (K or Na) is so powerfully reactive, the reacted form (K+ or Na+) is tremendously inactive. its one of those quirky duality things in chemistry.
You'd have an incredibly tough time reacting them even if you wanted to.