It was never required to be named after a saint, but many parents chose to name their child after a siant. That saint became their child's patron, and is thought to look after the child in a special way. It is the same with confirmation names as well.
There is no saint in the Catholic tradition named Saint Tatum. The name Tatum is not a commonly recognized saint's name.
No, there is no saint named Kennedy.
I can find no saint named Chelsea.
There is no saint named Shined.
I can find no canonized saint named Cassandra.
There is no saint named Ellen. However, the name derives from Helena and there is a saint named Helena
No, Muireann is not a saint name.
There is no saint named Ashling.
There is no canonized saint by that name.
There is no saint named Lee.
There is no saint named Macy.
There is no saint named Meredith.