(a) Is there any basis for justifying the action of the young kohanim in jumping into the flames after surrendering the keys to the heichal?
(b) Also, how did the Roman official obtain olam ha ba if he committed
suicide, as that constitutes murder which is forbidden to bnei Noach?
(a) In order to prevent being tortured and forced to abandon Torah and Mitzvos it is permitted, as we find in the case of Shaul and Yonasan. See DA'AS ZEKEINIM in Parshas Noach (Bereishis 9:5), and TOSFOS in Gitin (57b).
(b) It is permitted to give up one's life for the sake of saving all of Klal Yisrael (RITVA, Kesuvos 18b). Also, some permit giving up one's life for any Mitzvah, as a Midas Chasidus, although it is not required (RITVA, Chulin 101b; SHITAH MEKUBETZES, Kesuvos 3b).
The Minchas Chinuch permits a Ben Noach to commit suicide.