I have knob & tube wiring connected to a couple of standard breakers. Is it code compliant to upgrade the breakers to dual Afci/Gfci breakers instead of at the circuit end (at the receptacles)?
Yes, you're generally allowed to do more than the "slumlord bare minimums" that Code requires.
Installing AFCI breakers doesn't introduce any new Code complications. Though it will start detecting arc faults and ground faults that were previously happening totally undetected, and suddenly detecting them can force you to fix them. Sort of like buying a radon detector for a basement that never had one - surprise!
If code compliant, can I use standard receptacles on each of the dual breakers?
When you say "standard" do you mean 3-prong outlets with the ground holes so you can plug stuff in without cheaters? Yes, since they are GFCI protected at the source.
Do I then have to still put “no ground” and “Afci/Gfci protected” by the receptacle?
You're describing the picture postcard example of where that labeling is required. Of course you do, this is the very definition of when you need to use it.
However, the ugly blue stickers are provided only for your convenience. If you don't like them and want to use a more tasteful labeling method, you can use any you like as long as it is legible and not handwritten. It must say both
- GFCI Protected
- No Equipment Ground
If you don't want the "GFCI Protected" label, then use an AFCI breaker and stick GFCI receptacles at each socket. If you don't want the "No Equipment Ground" label, then actually retrofit grounds - NEC 2014 greatly relaxed the rules on doing that.