27 year old dating a 17 year old

So we have an open dhs case with my fiancé's two kids due to their bio mom using meth. Dhs keeps giving their mom more and more time with the kids. She never completed drug treatment as ordered she dropped out 2-3 times. Dhs drug tests her every few months but won't release her drug tests to our lawyer, social worker says she's clean but where is the proof? Mom then brags about using fake piss shoved up her vagina!!! She also brags about going back to meth as soon as the case closes... really? She texts my fiancé she's mentally unstable having nightmares and not sleeping. This woman hasn't been clean even a year! We have brought this up with the social workers and they brush it off . Plus dhs thinks it's cute for a 27 year old woman to date and fuck a 16 year old boy (just turned 17) dhs turns their heads at so much shit. Whatever happened to what's in the best interest for the kids? Spending all this time with their mom for her to return to the shit she was doing? Confuse and hurt the kids more. She's come and gone out of their lives so much it's sickening... we try so hard to protect them but dhs just keeps giving her more and more! This lady even had the balls to pick up her kids from daycare without car seats!! Kids are 6 and 3 years old... their mom was asked to prove she is working by our lawyer and social worker says she doesn't have to. She's told everyone she only wants split custody because she doesn't want to pay child support! I'm sorry but you will have to pay child support you don't live with the kids and they only visit her... I'm sorry but two visits one week and 3 including overnight on the weekend is plenty. She doesn't even live in the same school district and wants over nights during the week which my states laws state she can't have overnights during the school week if she lives out of the school district! The stress is killing us. This woman is an ugly human being!