Is this even possible?

My step daughter has just came into our custody permanently recently. We had temporary custody for a year. Meaning the court found her mother unstable enough to care for her. Now my 5 year old is hearing she is getting a sibiling. Her birth mother and wife are adopting. But they haven't taken the mandatory adoption classes. Can they adopt a child of they lost custody of her birth child? Just concerned because her mom is already saying things to my 5 year old like "you're My favorite until the new baby comes" ... I'm worried they will leave her broken if/ when this baby comes in November