You don't need to have gained 5 life all at once to satisfy Resplendent Angel's triggered ability
Our options are therefore as follows: Azorius v Jund: Will, Scion of Peace & Ikra Shidiqi, the Usurper + Kediss, Emberclaw Familiar Rakdos v Bant: Judith, Carnage Connoisseur & Shanna, Purifying Blade Selesnya v Grixis: Trelasarra, Moon Dancer & Solkanar the Swamp King Boros v Sultai: Firesong and Sunspeaker & Zimone and Dina Golgari v Jeskai: Beledros Witherbloom & The Archimandrite Okay, there should be six, but if you can find an oppositional pair in Dimir and Naya that can both be reasonably called a life gain deck, go for it
If the copied token is copying something else (for example, if the copied token is one previously created by this ability), then the token enters as whatever that token copied
Specifically, the undying ability triggers when the undying creature goes to the graveyard