When I moved house, my DPs used to do this every Saturday & Sunday
. Just turn up, no phone call or text, no respect for boundaries, no concept that the weekend was family time i.e. mine, DHs's and DC's!
Our door doesn't have a Yale type lock, and we use the back door, never the front. It needed to be open for DCs to be able to be in and out, to play in the garden, to check on animals, same as OP's door. So if no one was in the kitchen, which overlooks where they park their car, we wouldn't know till we happened to walk in the kitchen, where they'd be sat!
It was driving us to distraction. No subtle hints registered, or if they did they were ignored. It was the fact that I never had the opportunity to say it wasn't convenient that pissed me off, and the consistency of it.
Eventually, I had to be very blunt, and said you need to let me know, not just turn up, and coming every Saturday & Sunday is too much. Now they barely ever come, unless they're dropping my DCs off, and I obviously know that is going to happen. Be blunt OP, your DPs sound like mine.