Bayleef won't be any good offensively, but can be used as a support for this battle. Leech Seed would be useful here, or moves to put to sleep or paralyse. Also a meat shield you can switch to in case of someone else getting confused. Heracross in Gen 2 can't aid itself with TM moves like in later games, not sure where you get Thief. Slowpoke could be evolved into Slowking if you have the means, then its Psychic attacks should have some more power along with some added bulk. You could try using moves like Flash/Attract/Swagger on Morty's lead and give Slowpoke a chance to setup. Eevee gets Bite at level 30 if you're prepared to grind it. Steel or Ground might be a good edition to your team, or perhaps evolving Eevee into Umbreon once it gets Bite.