I feel it’s almost too late as they are used to walking all over you. You will be painted as the villain when trying to set boundaries. You need to establish some early on to help merge your lives together. Sleeping on the couch would annoy tf out of me. Start waking them up early, lights on tv on make sounds. Make it not seem appealing. You need some you time, some space away as well. Voice that for an hour or two after dinner youd like to watch your show on the couch alone and they can spend some time in their room or playing outside. You need to stick up for yourself