Sleep training

Twin mommas I need some help. My twins are 6 months and sleep great through the night and have been since they weee 2 months. My issue is one of my girls is great at self soothing and will sleep un swaddled and in her crib by herself. My other girl still needs to be swaddled and be in her swing to fall asleep she doesnt self sooth. Please help she can't be swaddled and out to sleep by her swing forever. She does stay a sleep when she is a sleep and moved to her room but has to be rocked. Help!!!