For Multi AI you run Life Orb Metagross lead and Sash Chomp in the back. They're the same sets in the singles team pins, only difference is that chomp runs Dclaw instead of outrage and Meta is Adamant Max Atk Max Speed EVs.
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In general, you want to get partners for your mons that are levitators or fliers that don't get hit by earthquake, and this is ESPECIALLY IMPORTANT FOR THE LEAD PARTNER! The Latis, Legendary Birds, Cressellia, and other good fliers are the keys here. If the backline partner is also a good flying mon, that's great. 2nd best type of partners are super bulky mons (usually normal types) that can easily live EQs from Meta and Chomp like Snorlax, Slaking, Porygon 2, Suicune, etc. The 2 best NPCs are Mira and Cheryl. Riley can allegedly be good with his dragons but has a tendency to be inept. Marley frequently runs at least one mon that is inexcusably bad, and Buck should basically never be chosen unless you do so in Diamond/Pearl where he can sometimes have actually usable fat mons like Cressellia. Otherwise, never choose Buck or you will die to regret it.

Metagross @ Life Orb
Ability: Clear Body
EVs: 252 Atk / 252 Spe / 6 SpD
Nature: Adamant
- Iron Head
- Earthquake
- Explosion
- Bullet Punch
Meta is the de facto Multi AI lead because it's too good at controlling the battlefield by itself with a get out of jail free card in Explosion, priority bullet punch to oneshot faster frail threats and do damage before it gets KO'd, and with its stab iron head that hits soooo many mons that give Chomp trouble. Primarily it will be spamming EQ while its flying partner helps it pick up kills. 

Garchomp @ Focus Sash
Nature: Jolly 
EVs: 252 Atk / 252 Spe / 6 SpD
- Dragon Claw
- Swords Dance
- Earthquake
- Fire Fang
Chomp does his regular thing of hitting the field and killing as much stuff as possible before it goes down. You have a sash so that it's possible for you to still boost up with swords dance, but you could run rock slide over SD too if you want more coverage. The goal is to decimate the enemy team as much as possible before Chomp goes down so that your AI partner can easily clean up the rest of the fight on their own. 
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When you get to battle 50, drop Chomp and put your RM in the back with a sash, and teach them protect to hopefully absorb moves for your partner to live longer if Meta gets owned early on.
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Psychic J Note: a status move is usually worth having (like Toxic or Thunder Wave) if the Pokémon isn’t that great for battles, otherwise a decent STAB/coverage attack or priority attack. Since this is a Multi Battle format, reminder that the opponents are 2 trainers with 2 Pokémon each, which means you can target down one side to turn it into a 2v1 once you clear out one trainer's 2 Pokémon.

OTHER NOTES
The main things that matter when it comes to the partner mons you pick are two things
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1. Does the mon prevent my own mons from using Earthquake (ESPECIALLY important for lead partners)?
2. Is the mon hot garbage and will not help me at all and/or be a complete sandbag deadweight if it was the last mon standing (more important for second partner)?
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Factor 1 is the more important of the two, but I think settling for a shit mon in the back during later sets (alakazam, roserade, lucario, etc.) is not worth risking considering how long making a multi AI streak takes, and one should just reset the available mons till better partner mons show up.
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If you need to reset the partners' mons that they are offering, go and purposefully tank one of your other tower streaks by forfeiting. Singles is the best for this since you can only get the palmer ribbons once per streak anyways.