Leafeon at a separated area in the southeast part of Chrysolia Forest and Glaceon in a part of Celestinine Mountain accessible from the northwest part of North Aventurine Woods. You should be able to see their respective rocks once you get there.
In Reborn the Move Relearner only teaches moves from levels less than or equal to your current, so you'll have to wait until level 85 to get Parting Shot.
Did you try hatching the egg in South Obsidia Ward? For a lot of the quests where you need to return Pokemon and stuff you can work around it by just hatching it in the same location you got the original.
If you buy enough ice cream from a vending machine then you'll eventually get one for free. The other ways are from Pickup and from the ice cream vendor in Agate Circus where it's supposed to appear in the shop itself every once in a while, but I've never seen that for myself so I don't actually know how it works.
I think you might be able to go around behind those trees from the left side to get it. Otherwise, you can probably walk down on that plant path from the top, but you're definitely able to get it once you obtain Surf and can come back.
Btw if you hadn't been able to solve it you can get Pixie Plates from mining and you don't really need the Luck Incense if you get the Amulet Coin from the Scrapyard in the desert.
For Pumpkaboo I believe you need a Soul Candle (purchased from 7th Street) and then to talk to the pumpkins at night.
Tyrunt and Amaura should just be a Farfetch'd and Pidgeot, but I guess if you can't get another Helix Fossil then you would need the trade (btw if you do have a Helix and it still isn't working then put all your Dome Fossils in the Item Storage in your PC).
To get to that floor you have to obtain all 10 available Department Store Stickers. Here's a link to how to find them:
https://pokemon-reborn.fandom.com/wiki/Membership_Card
You can also find a Protector in Iolia Valley if that's easier.