Many children who have experienced trauma and repeated moves exhibit regressive behaviors...that is because they never completed important developmental steps in a nurturing relationship in which contingent-collaborative communication and responsive care were abundent.
I have two suggestions.
First, you really should get the children evaluated by a competant professional/therapist who is trained and experienced in attachment and adoptive/foster issues. You can probably find someone in your region who is a member of The Association for the Treatment and Training in the Attachment of Children at
www.ATTACh.org That is important. Children as old as yours and who have been through what little you describe have adjustments and issues that need to be professionally identified so that you get the support you will need to help your children heal and connect with you and your family. Without knowledge of their issues and specific techniques to use, you are working in the dark. "Automatic" parenting (what you do naturally) frequently does not help such children.
Second, I would allow the regression. When children get what they need they do move on. My youngest daughter used a bottle up until age 7 or so and eventually just didn't need it anymore. My experience is that if you provide regressive experiences (do the things you would have done had you had the children from birth) you will go a long way to helping them heal and form a more healthy and secure attachment to you...let you take care of them and form an authentic affective relationship.
Best wishes,