Check-in cut-off in DUB for DL is 75 min prior to the flight, or 1 hr 15 min. 105 - 75 = 30 min. I.e. your parents will have a 30 min window to make the transfer and meet the deadline (and you didn't specify where they're coming from so it could include customs and immigration too), which includes claiming bags transferring terminals. As "Marco from Tropoja" says in Taken - "Gooood luck".