J.H.
wash fruits thoroughly and immediately when returning from grocery store. Many times the fruit flies are coming home with us and we can't notice because the eggs are there. Do not use citrus scented air freshners, we found that a can of glade citrus was covered with fruitflies left on the sun porch. can't say if that was from sticky hands on the can prior or not, but also wipe kitchen surfaces down well with clorox clean up and keep fruit in the refrigerator if you can. may not be the answer, but is worth a try. discard eaten fruit and peelings into garbage by tying in a plastic bag first and then discard into garbage can. Remember that potatoes make fruit flies (veggies) too.
Maybe the two of them (your parents) are just sweet as honey. If they are in this case, you can do nothing with the fruit flies.(smile)
Good luck to you.