I am looking to see what the pros/cons and if it is a good idea to swap out old 2 prong receptacles (that are connected to old knob & tube wiring) with dual AFCI/GFCI receptacles or swap them out with just GFCI ones.
I would guess that an accidental short circuit that sparks enough to start a fire is more likely in aging knob-and-tube wiring than in modern wiring. That's the scenario AFCI is intended to protect you against.
GFCI protects you against electrocuting yourself if the safety ground isn't there or doesn't do what it's supposed to do.
You can get combined AFCI/GFCI breakers. Or you can get an AFCI breaker and install GFCI outlets where desired, which may be less expensive (especially if a GFCI outlet can be used to protect downstream outlets rather than needing a GFCI at each location, but gods only know whether you can achieve that if you have K&T).
GFCI and AFCI have almost the same name, but so does methanol and ethanol :) The first one is deadly to drink, the next one is fun!
You are saying that you want the wire in the walls protected. AFCI is pretty good at that, being an arc fault detector.
However, you aim to place the AFCI at the end of the wires instead of at the beginning. That's like having TSA make people go through metal detectors as they get off the airplane LOL.
The GFCI is a totally different deal. As a ground fault detector, it does a pretty good job protecting humans from shocks by appliances if it is at the receptacle.
Thus an AFCI won't help your situation unless it's at the breaker or at a receptacle immediately after the breaker (and wired to protect the rest of the circuit, which by the way is a thing that both AFCI and GFCI can do; most people don't know that).
You should, if possible, protect your k&t wiring with dual function circuit breakers not outlets. GFCI and/or AFCI outlets will protect your wiring partially or not at all depending on where and how you install them. Combination breakers will protect against various in-wall failures throughout their circuits.