I need advice on how to deal with my family fued!?

ok so let me start by laying out my family history i have one half sister from my mom's side (Rose) and one half sister from my dad's side (Michelle) , then one full brother and im the youngest. Also my sister Rose and I live in Louisiana and my brother, dad and Michelle live in Florida. So with that information aside, about a year ago my mom passed away and my dad started dating this woman six months after! This lady went to high school with my mom and at first she seemed alright, but my sister Rose and i were shocked that my dad was moving on so quickly especially since we were still mourning our mom. Michelle on the other hand was more supportive of my dad (For the record before my mom passed i was close to both my sisters) Once it was clear they started dating my sister michelle became "buddy buddy" with this lady and started disrespecting my sister rose and I. And of course there became a verbal argument over the phone between all three of us. With me i feel like im in the middle between my sisters and between my sister Rose and my dad. Should i support my dad's relationship even though i dont like her? Then should i reconcile with my sister Michelle who has been rude when it comes to our feelings? I'm just cause in one giant emotional mess and im to poor for therapy so i thought i'll give yahoo answers a try..... what do i do????????