You have two choices:
The saint for whom you are named
The saint whose feast day falls on your birthday
However, for Confirmation you can choose any saint you wish.
I can find no saint named Kildans. However, there was a Saint Kilda but no information has survived about this person.
The person is canonized as a saint.
It means when did the saint get canonize or when did the Church declare that person to be a saint. Canonization/canonize is when the Catholic church declares a dead person to be a saint. It's a long and lengthy process to declare/canonize a person to be a saint.
I can find on reference to any saint named Scarlet.
Canonization is the process of declaring a person to be a saint.
Yes, Saint Augustine is a real saint. He was a Christian theologian and philosopher who lived in the 4th and 5th centuries and is recognized as a saint by the Catholic Church as well as other Christian denominations.
I find no reference to any saint name Alyssa.
They were, basically, declared a saint by popular acclamation. The declaring the person a saint was then made by a local bishop.
I can find no such saint.
When the pope declares a person a saint, it is said that he canonizes them.
I can find no saint named Siobhan.
I can find no saint named Chloe.