I will tell you what we believe about the passage, but first I think it's important for you to think about what answer you WANT to hear and why. You have consulted many teachers and pastors and yet still feel the need to inquire. That sounds like you're waiting for something you haven't heard, and/or don't believe the answers you have. I don't know what answer these other teachers have given, if we differ then we can't all be right. So the question is, do we have any more authority than they do in your estimation?
The passage in question, Matt 18:34-35, says, And his lord, moved with anger, handed him over to the torturers until he should repay all that was owed him. "My heavenly Father will also do the same to you, if each of you does not forgive his brother from your heart."
This passage is one of many which show how Jesus was revealing how the Pharisees and rulers were not right before God even though they boasted in their public works. He used these parables and statements to say they needed something more or they would not be saved. Other statements include sayings like "judge not, or you will be judged", "he who looks on a woman with lust has commited adultery in his heart", and "unless your righteousness surpasses that of the Scribes and Pharisees, you will not enter the Kingdom of heaven". If you take these (and many others) as requirements for salvation, you'd have an unacheivable list, and we understand that salvation is by faith and not by works. That is why we know that Jesus was talking to those who thought they were righteous to show they weren't and that everyone needs a Savior. Of course these statements are important, Jesus has underscored that this is the kind of heart and action that God expects, but not for obtaining righteousness or salvation.
Then the clear statements about salvation make sense such as John 5:24 "Truly, truly, I say to you, he who hears My word, and believes Him who sent Me, has eternal life, and does not come into judgment, but has passed out of death into life." or Rom 10:9, "that if you confess with your mouth Jesus as Lord, and believe in your heart that God raised Him from the dead, you will be saved;" or Rom 8:1, "Therefore there is now no condemnation for those who are in Christ Jesus". Now, as clear as these are, it is not always clear where a person's heart really is, especially when their life doesn't show a change. But it's not doctrinally sound to point at one practice or attitude and decide on that basis that a person has not been born again.
It's impossible to give advice about the unforgiveness and alienation that have plagued your family. However, I will venture this: forgiveness often starts with grace being extended by the righteous person. Everyone certainly knows what everyone else thinks about the issues by now; there's no reason to keep beating that drum, and apparently, it hasn't worked anyway.
Hope this helps!
Pastor Dan Holgate
Calvary Community Church