So right now you are not a foster family, right? And CPS, knowing that you are caring for your niece's children, is OK with you not doing so through the foster system? But if your niece shows up to take them back, then CPS will become involved and put the kiddos in a foster home? And then you'll be in the whole "work your plan" situation unless and until tpr happens? So you are being pro-active in trying to get rights terminated without the CPS involvement?
Did I get that all correct?
If so, I hope you have an easy road ahead! (Are the kiddos in counselling yet?)