Oh boy, in advance my apologies for mis spelling grammar and run on sentences! Hopefully I can express and explain my Dilemma my possession as a step parent to my stepdaughter who I have concerns for. I'm not stepmom I am a "guardian" in her words! But she call her moms boyfriend now fiancé who been together for two years dad! She is with her mother full and we have her every other weekend my partner( her bio dad) and BM#2 who is the mother of stepdaughter I'm about to address my concerns and issues in a few! Have verbal no court order agreement that he would have the same rights as he has a court order with his first daughter. But she enjoys using taking him to court so she can have her way and pretty much keep or not allowing him to have their daughter as they verbal agreed! Or because of something their daughter related back when she would get her and she would complain on how her sister treated her or how she doesn't do anything at dads beside relaxing at home and would threat court n he would just allow her and bend down to let her have her way! 
in the begging of our relationship I felt that my involvement in their child was important and respect I was included in the coparenting and I done my best to do fun stuff with the SD's come on their weekend so they are kept busy! But years pass and started to feel I was being envy and girls adored me n enjoy the weekends n BM# would cause little flare of fights n threat to take him to courts and he don't pay child support n how she commidates his needs (but he would pay for stuff if the daughter needed things at her moms but the mom wouldn't not ask him. Unless asking the child derectly if she needed anything at her moms n he would get it! 
so end of 2018 BM#2 pretty much gave him no choice and played the fear card of courts to now been two years in a row for us no have her the break afrom Xmas to the New Years. Once he said he didn't allow their daughter to go, He did once about saying no cause is taking away his time and bonding with her! She would keep her from him anyways n threat take me to court till then u won't see ur daughter! Well this last year New Years they had taken a pictures in New York stepdaughter BM#2 and moms now fiancé (they dated less then 3 years but when I raise n spoke to wrong person related the info too BM#2 about how unappreciated her man was holding and the kiss on the mouth (which triggered sever ptsd of my own childhood trauma. The way stepdaughter acts also concerns me since Iin a way I see my self in her, when the person I vented and asked for advice from screened shot and send it to BM#2. It was a mess she pretty much put me in my place and how i am no body to care or think that of her child! Since we aren't married n only have our daughter at the time that I am no body to accuse such things and how wrong I am to think that n to stop doing what I was doing or she will keep her away from him cause of me and to prep cause he will have no right n how he knows she comes from money and he gatta work hard for his that can't even afford to win,  but he do her the favor of losing and fucking him over. within the year each time we had stepdaughters The daughter im still talking anout has purposly harm in injurying my dsughter who has mitocandrial deases (chromic illness) she keeps a look out for me for when i come back to them  or if im nog bpaying attention, will take the Opportunities  to harm my child by biting, pinshing, pushing and most resort chocking!!! I'm at lost don't know what to do n how to go about it! I try to understand her actions n could be it be one of many point as too why she is acting the way she is but is just more then simple jealousy she is progressing and becoming more aggression goes with my daughter n i am don't on how BM#2 is only one allowed and pull his strings and get her way! I fear for my child life who I am 24/7 caring for her medical need sleepless night stressful hospitalizations! To be just taken away in a split sec I turn my back being in same room couple feet apart. I started to dislike her and hate her due too her actions and her mother even my partner (her dad) way of putting and disacluding me in a spot of no body who's input don't matter! I can't deal with no explainssion as too why she does that and a slap on the hand not even now is more a serious talk so she can understand what she done was bad but she continues but is now sneaker from last last time she had done an action of hurting my daughter. What can I do as my own kids safety and the concerns of my SD acts! They put me down as I don't what I'm talking about or how dramatic I'm overly am, I'm over reacting, how they simply justify her by poor her she is with mom full time have her all to her and undivided attention n then comes to dad n gatta adjust too sharing the parent n more with our daughter. N how she doesn't fully understand her sister condition and as too why she needs the attention. But this time how she chocked her come on I can't let it just drop like a simple bite or a push this more now! She has lie and loves to lie even to her mom and as well steal things cause she liked it and wants one... what can I do that I won't cause my partners loss his daughter! I wanna help to where BM#2 don't have anymeans leverage of blackmail to get her way and keep pulling that card of fear and as well the safety of that child of their if  is more to save her before it become worse and too late!