BLENDED FAMILY HELP!! Long post SIA..

My mom and her boyfriend have been together almost 7 years now. My mom has 3 kids- me & my two brothers, and my stepdad has 2 kids- my two step sisters. It seems his daughters have always had some sort of issue with my mom. Lots of drama/fights inbetween these years but fast forward to today.. things are only getting worse. His 2 daughters think my mom has no say in any parenting (example:my stepsister and I are going to college next year and she thinks my mom shouldnt have anything to do or say with her finances with schooling- and their mom agrees) I personally think their mother is the one to blame with a lot of these issues but that's another story; his daughters would basically be happiest if he and my mom just broke up. MY QUESTION IS: What can I do?? I tell her to sit everyone down for a family intervention but she thinks there's no point as she'll just be attacked the whole time. Can i sit down with them? Like a kid family intervention? Something needs to be done.. I'm not one for drama so I try to seperate myself from all this but nobody else is going to do anything. Ideas/advice/tips.. ANYTHING would be helpful. :(( Thankyou!!