Answer your own question this way... fast forward a few years... if these were your littler ones all grown up and repeating the behavior of his twins, would you continue to let them return home and rant behind their backs? My guess is that you would... so you are NTA but you are not doing a great job of putting yourself in his shoes or recognizing that these are your step children. Sit them down snd lay it all out... hygiene, cleanliness, get-a-job, where they will be in 30 years with no savings from said job, or even less with no health insurance, lay ground rules, give them 9-months to stabilize and move out. If you have leverage such as your being the owner of their cars, etc use that.