Changing the locks is expensive. It is about the same price as purchasing a new locking doorknob and deadbolt.
May I suggest that you pick up a Kwikset Smart Key lock combo?
It makes it simple to rekey your locks yourself, as often as you want, to any housekey you wish.
You could GIVE them a key, and then make sure it only works when YOU want it to work.
You've never seen a front door lock like this? https://www.amazon.com/dp/B00YMFGN00/ref=cm_sw_r_apan_i_31VTSADPGQ9G1DFCX3EX?_encoding=UTF8&psc=1
Every house I've ever lived in and most I've been to had door locks like this.
If the twisty thing in the knob is horizontal it's locked when it's closed.
Real easy to lock yourself out.
I recommend something like like the Kwikset locks because they make rekeying easy and cheap.