I sympathise OP. For years staying at PILs was something I dreaded. They were well off and still relatively young (70s) but it was incredibly hot, TV on all day at ear-bleeding levels, grubby bathroom, tiny meals, uncomfortable bed, uncurtained window, crap shower. Three or four days of heat, constant noise, poor sleep, early waking (either dawn light or their radio alarm on at full blast at 6.30am), aching backs and not enough food made us both feel quite unwell. It seems trivial but not being able to have a decent shower and wash my hair made me feel even worse.
Fitting into PILs rigid routines (it felt like the sky would fall in if The Coffee was not at precisely 11.00) was a strain and listening to, never mind trying to take part in, conversation with two increasingly deaf people was exhausting. They lived in the middle of nowhere with no alternative accomodation nearby. I started packing extra food so we wouldn't go hungry, some black-out fabric for the window and a small duvet we could sneak under the bottom sheet to make the bed more comfortable.
Eventually dementia and a house move meant that staying with them was no longer viable. When we stayed elsewhere we didn't feel tired, hungry and snappy and the time we spent with them was better.
FIL is now on his own and a spare room is available again. DH stayed there on his own soon after MIL died. Different house but the issues of heat, TV noise, deafness, uncomfortable bed, lack of food, grubbiness, poor shower are the same.
There is a very nice Airbnb within 5 minutes drive which we stayed in while MIL was ill. But since her death I think FIL and DH are expecting we will stay at the house from now on.
But I don't want to set a precedent for this new phase. I am going to book the Airbnb and major on not wanting to put FIL, now in his 90s, to the trouble of two guests with all the bed linen, towels, food that entails. I expect FIL might be surprised and maybe even a little hurt but, however much he would like us to stay, he is very elderly now and not a natural host, and we will all have a more pleasant visit if we don't.
I'm expecting it to be slightly awkward the first time but it's for the best in the long run. Just go for it OP. Use whatever reason you want for the first time (work, DS's girlfriend, WiFi) say how well it works and after that it just becomes the norm.