How to Find Angle of Armature Current
a-) Each generator share the load equally. Each generator's load is 450 kW.
First of all, calculate the total load current:

$$I_{load} =\frac{900000}{\sqrt{3}\times11000\times 0.8}=59\ A $$
$$\vec{I_{load}}=59\ \angle{-36.87^\circ}\ A $$

If first generator's load is 450 kW, the power factor of this generator easily calculated as follow:

$$\cos \phi_1=\frac{450000}{\sqrt{3}\times11000\times25}=0.9447$$

and the angle of power is $$\phi_1=19.13^\circ$$
The total load current is the vectorel sum of two generator's current, i.e:

$$\vec{I_{load}}=\vec{I_1}+\vec{I_2}$$

So the current of second generator is

$$\vec{I_2}=\vec{I_{load}}-\vec{I_1}=59\ \angle{-36.87^\circ}-25\angle-19.13^\circ$$
$$\vec{I_2}=36\angle{-49^\circ}\ A$$

The remaining parts of question are easily solve from here.