[uvcyclotron]

I am having problem with this question where the same reaction mixture leads to different products under diff conditions.

I have no clues about reaction 1 

For reaction 2: I guess the the reaction follows an azo-coupling route...?
http://en.wikipedia.org/wiki/Azo_coupling

For reaction 3: I think the strongly acidic medium converts the -NH₂ into -NH₃⁺, which being a meta-directing group, leads to Ph⁺ addition via EAS at the meta position.

Correct me if I am wrong, and please suggest some mechanism for the 1st reaction.

[SVXX]

Basically azo-coupling is done in slightly acidic medium because excess acid attacks the diazonium ion itself, which is basic(as shown in pathway 3). Hence the rest is as you describe.
The product you state in pathway 1 is a by-product of azo-coupling done in slightly acidic medium. The lone pair of aniline acts as a Lewis base and facilitates diazonium attack on itself. The aromatic diazonium ion does not attack the lone pair of nitrogen in secondary and tertiary cases due to steric hindrance, so there product 1 becomes a minor product.
Pathway 2 is the usual azo-coupling product. The diazonium ion attacks benzene in an EAS reaction.

[uvcyclotron]

Basically azo-coupling is done in slightly acidic medium because excess acid attacks the diazonium ion itself, which is basic(as shown in pathway 3). Hence the rest is as you describe.

So do you mean to say that what I've inferred about the EAS mechanism for Q.3 is correct?

And thanks for the help in reaction 1.