Are they powerful enough to defeat the ToS team?

No, KH3 will be a tragedy.

Who knows. Knowing Kingdom Hearts there will be a huge plot twist to see who wins

Not at first- the legend/prophecy/whatever says that darkness shall emerge victorious at the Keyblade Graveyard, so I believe Sora and friends will lose there

 

After the worlds fall to darkness and all hope seems lost, though, the Guardians of Light will rally and finally defeat Xehanort and friends right before the game ends

 

Sounds a little cliché to be honest but I wouldn't put it past them, hopefully the finale won't be this simple and clean though

I should hope so

I think as we seal keyholes in KH3, some of the seekers will try to get in the way and six of them will be beaten. In the end of the game it's an even 7 on 7.

ToS? Tales of Syphonia? I'm assuming this isn't about KH III since it's in random. 

I havn't Played ToS to I can't say.

Not at first- the legend/prophecy/whatever says that darkness shall emerge victorious at the Keyblade Graveyard, so I believe Sora and friends will lose thereAfter the worlds fall to darkness and all hope seems lost, though, the Guardians of Light will rally and finally defeat Xehanort and friends right before the game endsSounds a little cliché to be honest but I wouldn't put it past them, hopefully the finale won't be this simple and clean though

Well, knowing how Nomura has done the series so far, the story will be complicated as usual since KH1. He likes to do Plot twists in every game, and seeing DDD this tendence wont be changed. I hope so, Nomura always surprise us in a manner or in another, and I like that so much.

no light yagami and his empire will finally fall

Sora and Riku can take them all on, no problem. They don't even need all seven guardians.

 

Even if the 7 do struggle they will have help from others like Donald and Goofy and all the Final Fantasy characters, so I think they could beat them.