Overall I think this team is good , but you should change it up a little. Here are my suggestions to that:
For weezing I would give him Black Sludge instead of Leftovers and replace Flamethower with Fire Blast and Toxic Spikes with Thunderbolt , Fire blast for mainly Ferrothorn.
Umbreon seems good and doesn't need changes , so I have nothing to say about Umbreon.
As for donphan, I would change the nature to impish otherwise Donphan is fine.
For Victini I would give it Choice Band insted of Choice Scarf and change its nature to Jolly. Also consider to change Zen Headbutt to Brick Break for Tyranitar and Heatran.
For Raikou, I would give it a Rash nature and replace Calm Mind with Aura Sphere and replace Subsitute with Volt Switch
And for Trevenant, I would give it a Brave nature. Otherwise pretty good
Try my suggestions on showdown if you'd like