I tip everyone who cares for my animals well. I want to build goodwill.
I wouldn't be thrilled about the son and girlfriend showing up without having been told about it. It's definitely unprofessional to send someone to your house who hasn't met the dog. I also don't see why they both had to go. Again, unprofessional to have a girlfriend tailing along.
But no harm, no foul. And you know these folks socially, if if only peripherally. Tip 20%, and if they watch your dog again ask about who all will have access to your keys/home/take care of dog. But bear in mind, good reliable pet care is hard to come by. So if you are happy with how your dog was cared for, then things are good.