It isnt part of the wedding. followign the wedding split makes no sense.
should be split 50/50.
Only reason to differentiate would be if one side is much bigger than the other say Chossons side is twice the size of the kallah’s side. Then the Chosson’s side should offer to pay extra , but the kallah’s side insisting on that is a bit petty
Though I can’t help but wonder if this is mashal of some sort. It seems so petty like Meir G said He agrees to pay 1/3 (~ $666) The other side agrees to pay $1000 they are fighting over $334 ?