Hi,
This is a simple 2 stage filly differential Opamp.
Input at the gates of M1-M2 and Output across RL.
There is only one differential input pair, M1-M2.
M1-M2 is the input transistors with M3-M4 as the current source load. The current is defined by the bias circuit involving M9-M10 and Ib.
M7 and M8 is the current source load for the second stage. The second stage input pair is M5-M6.
The gain for the first stage would be
A1 = 2 x gm-1,2 x (ro-1,2||ro-3,4)
The gain for the second stage would be
A2 = 2 x gm-5,6 x (ro-5,6||ro-7,8)
Total gain would be the product of the individual stage gains.