Hi, My little brother is stuck on the part where you defeate Misty ..

Your brother should train Charmeleon to level 35 at most because Misty's strongest pokemon, Starmie is level 31.

#1 Staryu is level 18
#2 Starmie is level 21

Your brother, Alex, should go catch an Ekans and/or a Pidgey or Spearow.

He should train them up to level 20 or higher.

He can catch them in the grass on Route 24 and 25. Make sure Ekans knows the attacks.

1.Leer
2.Poison Sting
3.Bite
4.Glare
The Pidgey should know
1.Tackle
2.Sand Attack
3.Gust
4.Quick Attack
And/or the Sperow
1.Peck
2.Leer
3.Fury Attack
4.Pursuit

They will also help a lot farther on in the game.

You should really go catch a Pikachu in Viridian Forest.

Then train it to about level 26-31.

Okay, what he needs is a nice Grass Type Pokemon with a Grass Type attack, like Absorb.

I suggest Oddish for this operation. He needs to Evolve it to Gloom, up to level 20.

I belive Oddish/Gloom learns Mega Drain sometime, but I cannot currently specify the level.

Well this is what I did.

I got mega munch from the guys that are fighting over mega punch and kick and I got mega punch and taught it to charmeleon.

If there is cool pokemon around catch them.

Train the charmeleon and get a high level Oddish

I beat Misty with a level 36 Charizard, I used the move flamethrower (not very effective but it takes more then half of its hp.