getrawmempool will give you all transactions "txid" in mempool.
then you need to run
getrawtransaction "txid" 1
it will give you detailed transaction in json.
from that you can get
"vin"
"vout"
fees = vin - vout
do this for all transactions and you will get fees of all transactions in mempool.
hope this helps.
no, txindex is required only if op wants to query old tx which are in block, but he only wants to query which are in mempool.,
so imho txindex is not required just to query tx in mempool.
in the mempool or relay set
pertinent to addresses in your wallet
pertinent to your "watch-only" addresses
ref: https://bitcoin.stackexchange.com/a/37979/10603
or maybe i am missing something.,
sorry for my bad english.