200 x 2 = $400 for 2 kids.
Can you justify that your both kids NEED more than 400 a month?
If you can convince yourself, then drop him a without-prejudice email with justification (Reasons)
If the decision cannot come to an amicable arrangement. You may consider proceeding to family court and pay $1 dollar for mediation.
I know a few case where woman gave "something" in exchange for sole custody of the children. If you did, then you might want to reconsider your position now and then.
PS: The above are not legal advise, just my opinion.
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