Suppose that I have a Transaction A. (txA) I send my txA to bitcoin network and full node validate it and put in Mempool and starts to broadcasting it.
A Miner A connect to a fullnode to create a candidate block and wins the POW. In this block there is my txA
A miners B create another block with all different transactions except to my txA.
If block A and block B have the same previous block Hash it's a fork,and if the chain of block A wins, all transaction of block B return to mempool.
But if B Has the previous block hash of A ? After create a block there is another check of all transactions? When TxA is in mempool it's unconfirmed when become confirmed?