Kinship now Foster placement - Intervening

My wife and I took custody, through kinship care, of her cousins kids back in June of this year. The youngest if biologically my wife's cousins daughter (bio dad) but the oldest is his step daughter. Since they are a sibling set we were allowed to take them through kinship care. We just recently became a licensed foster home at CPS recommendation (for adoption). The children were both removed for physical abuse and psychological abuse. In the 4 months the girls have been with us we've been privy to quite a few disturbing details. Within 3 weeks of being placed with us, a behavioral psychiatrist diagnosed the oldest with "Chronic and Severe PTSD" and the youngest with Fetal Alcohol Syndrome. The bio's adamantly deny that bio mom drank while pregnant and also argue that the PTSD diagnosis is false (we are having them evaluate again). There is also speculation of sexual abuse of the oldest based on statements she's made but when a forensic interview was attempted the child shut down. We've also been told, by both girls, that "time out" included being locked in their room all day (with no access to food or bathroom) which explained their WILD reactions the first time we mentioned they would go to time out if they kept misbehaving (since then we've adopted "time in" as the new norm). Every therapist they've see (currently in play therapy, behavioral therapy, and trauma therapy) has said the oldest is the worst case of PTSD they've seen in their careers. We've made huge strides in improving her overall behavior and demeanor in the 4 months she's been with us. Both girls call us "mommy" and "daddy" (we do not encourage it, we reinforce "Aunt *****" and "Uncle *****") and have said they would love to live with us "forever". So to my point...CPS has recently hinted that reunification may (I emphasize "may") happen with bio dad (parent getting divorced and bio mom not completing program) but he was one of the worst abusers of the girls (he's openly admitted to us, on the phone, of physically abusing both girls because he "lost his temper") and truly believes that 4 months of therapy has "heeled" him. We don't buy it and fear for the long term mental health of the girls. We were recently told that intervening may be our best bet to prevent them from being returned. Since we are biologically family to one of the girls...would we be more successful in intervening? Do we have a "stake" to intervene after only 4 months? Do we risk pissing off CPS and losing our foster license?