Can somebody tell me how to get to the ninth Rainbow Islands?

A Deoxys is a Legendary Pokemon with highly abnormal stats and you can only get him by getting an E-Reader or a Cheat Device.

This team has some pretty high levels (well, sort of) but if you are ever going to win, then you are going to have to give them both hold items, and a lot better attacks.
MY SUGGESTIONS:

Venusaur is pretty good but here are a few of my suggestions for it. Firstly, delete Strength and Razor Leaf. Both bad moves. Replace them with Synthesis and Sunny Day. Sunny Day is a must considering that Solarbeam only needs one turn and will get a power boost, and Synthesis will restore all of it's health. If this is your Starter Venusaur, then delete Hyper Beam for Frenzy Plant as it will get the type advantage. All grass moves. Well, that's not fantastic but these combo's are quite good. For Articuno, please delete that miserable Steel Wing as it is not very good at all.

Snoraz isn't that bad, but you should have kept Rest and Snore. Get rid of Ember and Fire Punch on Charizard and teach it Earthquake and Dragon Claw. Metal Claw is pretty useless as well so you may get rid of it for Heat Wave.

Lapras is good. Hitmonchan is a problem. All of those attacks really suck like hell. He has terrible atack anyway so I'd just get rid of him if I were you.

As for your brother...
He has trained all of his pokemon quite well, except for Jolteon. Anyway, all you need to beat the Elite Four is this
1 Charizard Level 73, one Zapdos Level 53 and one Articuno Level 52 +10 Full Restores and Revives. That's what I used.

Wow um.. I guess this is good. A few complaints though. First to get DSeoxys you need to be in a real life event. Next your team lacks style. Sorry. Let me give u pointers. First Venasaur. Take Out Hyper Beam. Try Sunny Day and synthesis since synthesis will restore all health with SunnyDay on the field and Solar Beam will take one turn to use. Articuno is good. Keep training it since it can learn the deadliest combo. Mind Reader and Shear Cold ! I guess Snorlax is ok but you should have kept Rest and Snore since it's a good combo.

Three FIRE attacks for Charizard ?! take out ember and fire punch. Also teach it Fly for fighting types and heat wave (obtained by giving 1 or two mushrooms to guy on island 2) Lapras..keep training. Hitmonchan stinks w/ those atks ! His sp. atk is BAD ! trust me, it will never take him far later on. Try psycical moves like rock Slide. Put Rayquaza in your party. That will definetly help ! Your borther's team is ok. Tell him he needs to train A LOT more.

Here's my party so far, still needs training but can delete the elite 4 in seconds and yes the second elite 4 !

Blastoise -
Surf, Hydro Cannon , Ice Beam , Earthquake Lv 77

Dragonite -
Fly, Ice Beam , Thunderbolt, Dragon Claw Lv 72

Kadabra -
Psychic , Shadow Ball, Recover, Calm Mind Lv 65

Snorlax -
Rest, Snore, Rock Slide, Body Slam

Primeape -
Cross Chop , Brick Break, Rock Slide, Dig

Electabuzz ! -
Thunderbolt, Brick Break, Iron Tail, TOXIC