It's entirely up to your older daughter and her husband if they truly do want to make that offer, but if they asked my advice I'd tell them not to. Your younger daughter will not appreciate any of it. She might say some nice things to get them to let her move in, but once she's there, she will rebel against them and their rules so fast their heads will spin. Maybe suggest that your older daughter attend a couple of Al-Anon meetings with you? You both could use some support!