Traveling with your adult kids and their significant others

New to this forum. We are traveling as a family (DW and 2 DDs) this summer. DD1 is bringing long time SO. Hopefully it will go well. it’s an 8 day trip so we have days that we scheduled that we are together touring but there are few days that are “free” for the DD1 and SO. Just to give them a break from us.

For the most part, we are paying for everything except for their expenses when they’re by themselves. We also offered to pay for SO’s flight but he insisted that he’ll cover his plane ticket. Which is nice.

Any advice for first time parent traveling with kid’s SO?