Rescue dog keeps going toilet in the house

Hi, I adopted 2 rescue dogs who were both used as lab research dogs. The girl we have a year and half but we only adopted the male 3 weeks ago.

The girls was relatively good and easy to train. BUT the boy...he was good for the first week with only the odd pee here and there. But now hes started going no.2 in the house aswell

We've used washing powder and white vinegar to clean and remove smells, then bought a urine remover spray but it seems to be getting worse.

We let him out for regular toilet breaks but it seems like now that he doesnt want to go outside. I had him out for a few hours and when he came in, straight away did a no2!!!

He's not your average dog as hes still very much traumatised from growing up in the lab so have to be carefull too how to train him.

Any advise would be much appreciated, TIA!!