You should not have to pay the other parties fees. Your modification is due to a change in circumstance. Especially, if there is an additional $100,000 to utilize, certainly no hardship!
I found this information concerning your inheritence question....
The Fifth District found that the trial court committed error when it ignored the reduction in living expenses that resulted from the payer’s having paid off debts and mortgages with a sizable inheritance. The court indicated that the reduction in living expenses warranted a departure from guideline support. The court noted that an inheritance or one-time gift is not income for child-support purposes, but interest, rent, dividend or other yield from those things should be considered as such.. In addition, the trial court has discretion to, but need not, impute income to the payer based on the interest that the inheritance might have yielded if it had been invested. County of Kern v. Castle (1990) 75 CA4th 1442. Similarly, a court must consider the value of rent-free housing and meal allowance in making a child support order. Stewart v Gomez (1996) 47 CA4th 1748.