Child Support - Mutual Consent Divorce

We are in the process of a mutual consent divorce. While arriving at terms, I have agreed to pay half of the schooling expenses for both my children. I have also agreed to pay half of the other expenses of both the children which has been mentioned as Rs.15000/ per month. We are having a problem at arriving at how to consider inflation etc for arriving at the increase in payments over the comings years. Question 01: How does one usually increase this agreed amount to factor for inflation? In the case of school fees, we have decided on a particular school and are the expenses are straightforward. In the case of college fees there is a huge uncertainty since you can have college fees that vary from even 1 lakh a year to 10 lakhs and beyond including donations/capitation. How do we usually set a cap on such figures? In this case the father is not very rich but the mother is from a rich family and has a huge inheritance. If the mother says that she want's to send the child for an expensive college, then half of that expenditure may not be affordable to the father. Question 02: How can this be managed/capped?