Here's something I want to throw out for someone to ponder, If a person has been divorced for a few years and the one parent that has custody of the two children both being under ten years of age ...
Punishing your children to right the wrong being done by your wife is a punk thing to do! She may be a jerk (although I'm wondering why she's being a jerk), but abandoning your kids would be the height of irresponsible behavior. Generally, when ex-spouses begin using the children as bargaining chips between them, it's because there is animosity, anger and venom between the two of them. USUALLY over infidelity!
What do you mean by: "try everything you can do to see them?" A simple court order will take care of that! If you don't have one, GET one! If you have one that she's not honoring, haul her sorry butt back before the judge 6 ways till Sunday, until she realizes that its in her best interest to comply with the court's order.
If you were unfaithful to your wife, the pain of your infidelity is no doubt the cause of her irrational behavior. But she's responding out of hurt; not a good, sound mind and reasoning.
If infidelity caused the break-up of your marriage and all of the subsequent aftermath, i advise you to rent the movie: Fireproof (with Kirk Cameron) and watch it. (It's real corny in some spots and has a real low budget film feel). BUT....the moral of the story is powerful! And it's one that so many people...male and female...need to see and hear!!! If after watching that movie you recognize yourself, do what the guy in the movie did. Your story probably won't have a "they lived happily ever after" ending, but sight unseen I can almost PROMISE you, that you will gain her respect and regain the ground that you need to start seeing your kids again.
If necessary, get a mediator to sit down with the 2 of you (AFTER you've done what the guy in the movie did, IF infidelity was the cause of your divorce), and work out an arrangement and scheduled for your parental days and times with the kids. (It may mean that a mediator...your sister/her sister, your brother/her brother, her mom/your mom) will need to agree to pick up the kids from her, bring them to you and then take them back to her, to avoid any unnecessary contact between the 2 of you.
It's really a shame when 2 adults can't set their personal feelings aside, long enough to support their innocent children. The average parent doesn't realize that EMOTIONAL abandonment does the same (if not worse) damage as PHYSICAL abandonment! Both plant seeds of rejection and abandonment in the child, which everybody pays for later on thru the child's drug addiction, promiscuity, law-breaking and a host of other dysfunctional behaviors.
If she chooses to continue behaving like an immature school girl, YOU be the mature person! Fight for your KIDS - not to prove any specific point to HER!