Two identical transactions and hashes in Block Hashing algorithm
1) Are the transactions 100% secure?


No.


  2) Suppose there are two identical transactions happening at the same time, are those transactions are going to get differentiated based on the Hashes?


Yes. It's difficult, though, because each transaction must include the hash of the previous transaction, and so on.

It used to be much easier. A while back, it was pointed out that two coinbases could have identical hashes, and so create identical transactions down the line. See also: Why block height is required in coinbase?