½ Spoon + ½ Fork + ½ Knife

That doesn't make any sense at all. If a T-1000 can't manage the job on its own, what chance does a T-800 have? There'd be absolutely no reason for them not to work together. And why would Skynet be deleted from the timeline if Carl is still around? Couldn't Carl hand himself over to the authorities, and say: "behold, all the technology which that idiot clone terminator kept from you when he self-destructed! I have last laugh, mwahahaha!" (laughs mechanically)

My lasting theory was that "Carl" was the failsafe. 'Carl' was never ment to fight alongside the T-1000 as it is presumed the T-1000 itself should be enough to kill John. IF it was sent back at the same time as the T-1000 its task was to observe from afar, and in the event the T-1000 failed it would resume the former terminators mission. Again assuming they both got sent to 95' my guess is rather than going after them when they are prepared 'Carl' thought the best approach would be to play the long con, it -is- an infiltrator unit after all and catch them with their guard down (which he did).

That T-800 was sent when the T-1000 was still alive.
Then what was he doing for 3 years? Because that scene takes place 3 years after
T2
. It makes no sense.
What a piece of ****.
Grade "A" Fully Loaded
"Sexy as Hell"

So why didn't they just send the T-1000 with 5 or 6 T-800s all at once to get John and Sarah? Lol. Why scatter them over different times?
They did. The opening scene takes place shortly after the events of T2. That T-800 was sent when the T-1000 was still alive.
The biggest plot hole to me was how “Carl” was able to live a secluded life with a family when “he” was wanted in 1984 for the police station massacre, and again in 95 with blowing up Cyberdyne. Yet, he managed he start his own drapery business and go evade authorities all this time.

I learned it in physics class.

When is that explained in the movie?
Grade "A" Fully Loaded
"Sexy as Hell"

It all comes down to the chrono unit which rests at the heart of the time machine. They are imprecise. You can send things back to an approximate date, but not to a specific one. This is just the nature of time travel.