There is no proper term for "Irish Twins" (a derogatory phrase by the way). They would simply be siblings.
Yes, siblings born less than a year apart are often referred to as Irish twins. This term is not accurate historically as it is not exclusive to Irish families, and the modern use of this term can be considered offensive.
Irish twins
Irish is the proper adjective for Irish, as in "Irish dancing," "Irish jig," or "Irish bar."
"Irish twins" isn't a phrase that's from Ireland, it's an offesive phrase used outside Ireland, so there's no equivalent Irish translation. "twins" is "cúpla"
Irish twins is a name given to a set of children in the same family who are born 13 months apart.
It is called a "Irish Twins" when siblings are born within the same calendar year but have different birthdays.
Irish
Caitlin is the proper way, the Irish way which is were the name Caitlin originated from. There are other ways but Cailitn is the proper/original spelling.
Anraí
"Irish tan" is simply a slang term for a sunburn.
One term is lassies.
leth-aonan or leth-chàraid