From what I've read in the other threads, probably right now there is nothing you can do because the custody decision is so new. You can't dictate what the other parent does with the children during their time unless they are in an extremely harmful situation. Then you could push the issue.
What? We're talking about child abandonment here. I would have filed for a modification after about 2-weeks regardless of when the last modification was. These are extraordinary circumstances and to have waiting NINE MONTHS to do something about it may actually end up looking worse than it would have had they moved sooner.
They should be filing yesterday.