Basset hound bathroom issues

Hello I have an adopted year old basset hound and we are dealing with issues when it comes to him and using the restroom inside the house.

For context at home we have a doggy door for him and he has no issue with going to the restroom inside our home. But because my spouse and I work opposite schedules we need assistance from our parents to watch him some days. That is because of separation anxiety. The reason for this post is because I need help and tips to help with his problem. He pees inside our parents homes even though they have other dogs that he gets along with and that there is access to a bathroom outside via doggy doors.

He has no issues some of the time but there are instances where he just pees on a bed or a couch. Is there anything anybody could tell me to help with this? Thank you very much.