So you are asking whether conditional proofs and RAA proofs (i.e. Reductio ad absurdum -->contradictory proof-->indirect proof) are elaborations of Modus ponens and Modus Tollens?

Honestly, they may look the same in format but they are nothing alike in structure (in my opinion). Modus ponens for example infers Q from P and P-->Q and thus only infers the consequent. A conditional, which requires the formation of a conditional, infers the whole thing, antecedent and consequent. Indirect proof wise, modus Tollens would have you conclude in the negated antecedent from a negated consequent. But in the case of the indirect proof, you can infer anything when you derive a contradiction. The Modus Tollens inference rule will only let you infer the negated antecedent.

On a side note, you may want to spell out the inference rule or the type of logical syntactical structure because there are many different ways of saying the exact same thing. Abbreviations are difficult to interpret in some instances, like the RAA abbreviation. I say this because in all honesty, I have no earthly idea what MI stands for. I see that it is a form of indirect proof from the structure and citation in 9.

As for the proof itself, you ask whether line 3 is correct. Line two is ok. You can do infer practically anything. But in line 3 you infer A & ~B by DeMorgans law from line 2.

DeMorgans can be done in two ways?
~(PvQ) can be replaced or replace ~P&~Q
~(P&Q) can be replaced or replace ~Pv~Q
So basically, switch the signs and negate the variables.

So you number 3 is correct as long as you negate both variables. You need to correct #3. This needs to corrected because you entire proof rests on the A wrongly inferred from line 3.

But line 3 would be ~~A v ~B. That's the same as A v ~B.

First, I think you probably mean (&) rather than (v) in you previous post. If line 2 has an (v), then line 3 will have a (&) or vice versa.

Though what you say is correct that ~~Av~B is the same as saying Av~B, that does not apply in this case. You are inferring Demorgans from line #2. The only way you can infer DeMorgans from line 2 is by stating ~A &~B. You are adding one negation too many to the antecedent. Also, you would have to cite double negation to get that in a previous line.

You cannot add that extra negation symbol until you have legitimately worked it into your proof through inference or replacement.