Good advice from Dold School-guy. I also would mention, putting a 2-stroke around loads up the silencer with unburnt oil, then ripping for a little while will clean out the silencer by blowing it out. Running real hard will get it red-hot and have it smoking like its about to catch fire. None of those are a huge issue really. Its not like you can tell the gf and her daughter to start ripping all the time or quit taking it easy and safe. Jetting to their style may be the answer. Keep your changes in mind when they start getting faster, or instead of rejetting, remind them to pull the clutch in and clean it out, when in the tight stuff, where riding speeds and rpm's are low. A little "brrrraaap, brrraap" with the clutch in, helps. Changing the packing every season with their bikes is a good idea, but that oil falling out onto the swingarm happens to all 2smokes at some point or another. It gets loaded up then cleaned out in a cycle. you just have to be aware that they do that.
That's a cool thing you're doing for them. I know that's alot of work from experience.