OP, other than continuing to support your ex wife ,it does not sound as though you have had to do anything that financially sufficient and parents vested in providing a good education and a good quality of life do not do on a regular and routine basis.
It seems as though you have not been as physically available and present for your children as they might have hoped for - given your travel schedule and the fact that you do not live near them.
You have met whatever obligation of support that you had to your ex. Now you need only provide for your children. What is problematic about your 16 calling to ask for funds. If he were living with you, you would not find that even remotely off putting.
My spouse and I , kept our premarital assets separate and placed them in trust for our respective children. We each owned property and had no need to purchase yet another home solely for everyday living. He moved into my house and we share living expenses.
I would assume that your new partner ,like yourself, is financially sufficient and independent. If there is not some pressing need for you to own yet another property, why not have him/her purchase their own home and you simply share expenses. This would prevent any need for you to become involved in any future estate issues.
My husband and I are going to purchase a summer place. This will be our first and only joint property purchase. We will purchase it as tenants in common and concurrent with the purchase we will each pot our interest in the property in trust for our respective children.
Perhaps you should meet with a lawyer or estate planner and get advice regarding a plan to manage financial resources in a separate and discrete pool .
Do not let anyone convenience you that you are doing more for your children than a good and well positioned father should and would happily do. Both my husband and my children's father generously support their children, but that was their plan and commitment when they each decided to have children, however, both married women who were equally committed to being financially sufficient providers in their own right.