What would you do in this situation - family divide????

ok so here goes.. my parents split up about 3 or 4 years ago - there are 4 children (all over 18) 2 of us only speak to my dad and 2 to my mother - but the 2 that speak to my mother use my dad when they want stuff... my mother - who was the one who went off wih another man is no trying to get our family home and kick my dad out... but as I dont speak to my mother my younger bro and sis are now being very nasty to me and slating me on their bebo sites and dont talk to me at all??? When I've done NOTHING on them... I know htis sounds very muddled... but wot shoudl I do?? should I just forget about them and let them be?? it upsets me greatly!!!