What can be done with a transaction with 0 confirmations, in memory pool but I've already double spent to complete a payment request. Will the original amount of bitcoin be returned to my core wallet? How can I clear the unconfirmed transaction from my core wallet? My wallet shows two different amount balances, one of which is a pending. However; the pending and total is less than the difference of the two transactions (first sent with too low of fee, and then the double spend with a higher fee). its off by about 0.01 BTC. Any suggestions... or is it just a waiting game to clear the transaction from mempool and then my wallet balance will go back to normal.
It depends which transaction will be confirmed first.
you can control your memory pool size with -maxmempool=n command, where n is size in mb (how i remember). By default your unconfirmed transaction will be deleted from mempool after 14 days from creation. Also you can use -zapwallettxes command to clear all unconfirmed tx from your wallet. (also you can try to delete mempool.dat file when your wallet if off and then restart it)
Also, read this good article - https://bitcointalksearch.org/topic/all-about-stuck-transactions-and-what-you-can-do-to-fix-them-1802212