How does someone deal with an estranged ex spouse when there is children involved?

My husband and I have been together for 5 yrs.I have two children from my previous marriage,he has one from his.Our children range in age from 7,9 and 15.We have been blessed with a wonderful family,and are all happy and healthy.Being a blended family is difficult at times,but probably no more then your "normal" typical family.However we both have one enormous obstacle in our lives,our "ex's".They are both very emotionally unstable people with alot of dysfunction.Except my husband's ex is psychotic, and she will stop at nothing but to ruin our happiness.My children reside with us,his child does not.He is with us almost half time.We are good parents,we both have very well established professions,a nice home,and loving families.Our children are our lives,and we work hard to be there for them.My husband's ex is trying to take away his rights to the visitation he has.She has lied to her lawyer etc.and wants to go to court for no reason.Very malicisous and vindictive she is.Someone help us?