Is there anything I can do about this awful situation.?

My dad was married to his ex wife for thirteen years. She had two kids that he essentially raised and was very close too. She dealt with some infidelity and mental health issues which resulted in her abruptly leaving and taking the kids on Christmas eve 2009 cutting up all contact. During the process of the divorce she accused him falsely of domestic violence against her ( which was thrown out for lack of any evidence). When she found out that he and myself were talking to the children she sent us threatening text messages which were vulgar and hateful..causing us to be afraid to talk to the kids (even though they attempt to see us by stopping by and texting us). My step sister recently sent me a message asking if she though my dad would see my 14 year old step brother as he broke down in counseling saying he lost the only dad he'd ever had. After she texted him asking if he would see my step brother he apparently told her he couldn't because his mom ( my dads ex wife ) threatened him against talking to the kids and his life was returning to normal. I think this is a horrible resolution which will result in my step brother feeling abandoned. After further talking to my step sister she assured me that her mom had changed her mind and was okay about us seeing the kids. Does anyone have any ideas about what to do? This is a horrible situation for all involved. We live in Ohio if it makes a difference.