Seán is an Irish name (translated to John in English). The name Eoin (Owen)is also used a first name and refers to the Biblical John
Sam is not an original Irish name; but Samuel is Somhairle (SO-ur-lyeh)
Justin - again not Irish - although it is shown translated into Irish as Saerbhreathach (SAYR-vrahok) although that looks wrong to me. It's on this website
http://www.namenerds.com/irish/ Cailey is a name I've never seen before, but according to
www.babeynamer.com it is a corruption of Caollaidhe (KAY-ul-uh) an Irish word meaning slender.
Another site says that Cailey is derived from the Greek for lark. Lark in Irish is Fuiseóg (FWISH-ogue) but I've never seen this used as a personal name