Family Drama Ugh : (

OMG, so much family drama, my sister Laura who lives in FL close to my mom, well my dad past away last year and my sister was very close to my dad, she's taking it really hard, she was also very close to my mom, they went shopping together, vacations always on the phone with one another. Well my parents had friends they hung around growing up, we went camping, card games and CB club, well Bob's wife died as well last year Bless their Souls, my mom starting talking more and more with Bob, well then Bob went to visit my mom, they started being there for one another, and my sister has taken this very hard, mom's not there like she use to be, well my sister and moms relationship has diminished, their not talking to one another, Bob is now with my mom, this year they traveled in a motorhome and came to visit me at this house for the first time, we got along well, I have always been distance from my adopted mom, she was very controlling growing up, treated me like a child for many years, like I said we had a good visit, but my sister told me alot of crap about how my mom was fake around me how she didn't want me around during my dads funeral just hurtful things prior to my mom's visit, well I just brushed it off, I went with the flow, now I feel like I'm in the middle, their not speaking to one another and my sisters being vindictive by writing off the wall crap on FB and texting my mom hurtful crazy things, and my mom would call me and ask if I have spoken to my sister, it's gotton crazy. I just want to live my life in peace. Why so much drama just go about your business and let it be, but Nooooo My sister is hurting, my mom has written her a letter basically saying she would be in my sister's life when she gets herself help with Alcohol, drugs and dangerous life syle, my sister is a mess, I don't want to talk to her much she will just take what I say and throw it at mom, and worried my moms stress level could lead to a heart attack.  How should I handle all this drama?