How do I focus on my kids and see my kids,if I am to see them at "their convenience." And using her term,"build your own relationship with the kids."
At the kids convenience? That's a laugh esp with teenagers.
Talk to her and the two of you set up a schedule that the kids stick to. there may be times when something one of the kids wants to do interferes, then it is up to the two of you to decide. Jointly.