How does fee split between senders in a transaction?

Question

I know how fee is calculated in a transaction, but I don't know how this fee amount split into senders.

For example, consider the following transaction with 0 BTC miner fee:

inputs:

   Alice    sends     20 BTC ->
   Bob      sends     10 BTC ->

miner fee: 0 BTC

outputs:

-> Carol   receives   15 BTC
-> Alice   receives   10 BTC
-> Bob     receives   5  BTC

Now if we consider 1 BTC for miner fee , how does these output amounts change?

Maybe in half?

-> Carol   receives   15  BTC
-> Alice   receives   9.5 BTC
-> Bob     receives   4.5 BTC

Answer 1

There is no real concept of sender identities, as far as the blockchain is concerned. The fee split is entirely determined by the change output values, which are entirely determined by the signers of the transaction.

A transaction involving inputs from two separate parties will require some coordination between them to decide on the recipient and change. It is presumed that during this coordination, a fee is decided upon, and set.

Bitcoin itself offers no insight into this splitting process, it should be handled out of band by the wallet or tool used to construct the transaction, based on configuration from the senders