At thirteen months old I wonder if it's dreams or just their time to wake up and cry because they don't see mommy. It's normal for some babies to wake up during the course of the night for feedings, diaper changes, dreams.
I read a few of your posts and they are in a strange place right now... and they need time to get used to it. I would imagine they knew they weren't with their mommy for a while and now they are. It could be a little insecurity on their part that they may be taken away for a spell again and because they can't talk or understand their emotions crying is the only way they can express them currently. It's hard to tell since they are so little and not talking. My best advice is if it isn't a diaper change, a feeding, or they aren't sick that they are crying about that they probably just need their mom present, regain that bonding and the security they should have and feel the comfort only a mother can give with her attention, hugs, kisses, rocking them gently to soothe them.
I'm sure there will be plenty of parents ringing in here soon to help you out. In the meantime I hope something I shared was helpful.