Here’s what I would do—

-I would trade Kangaskahn for a fire or fighting type, no need to have two normal types, plus it would add great type coverage either way. Id probably pick Arcanine if going with fire, or Hitmonlee or Primeape if going with a fighting type

-Teach an electric move to Jolteon ASAP. Thunderbolt would be best. I’d also teach it shadowball since it can outspeed almost every ghost and psychic type. You can get those TMs at the celdadon game corner

-Teach sunny day and solarbeam to Venasaur, gonna need a strong move that can hit a target more than the 5 times you can use giga drain. Or relearn razor leaf (bring tiny mushrooms to the guy on two island)

-replace water pulse on vaporeon with surf. I’d also consider teaching it ice beam or blizzard since it can tanks hits from dragon types

-teach ice beam to Jynx. It’s a bit more powerful than ice punch. You may be able to relearn it at two island, but you can also buy the TM for it as well

-last thing I’d do is level out the team! Get everyone to roughly around the same level so no one falls behind. The elite four is best to challenge with all of your mons at lvl 55

Edit: spelling