Correction
M24 and M26 are subject to ESD design rule. (same L, not minimum, extended drain contact distance to poly edge, non-mimimum source-side contact distance to poly edge)
M21 and M25 are subject to ESD design rule. (same guideline as above)
M23 tracks M19 Vth, including body effect.
M22 tracks M22 Vth, including body effect.
There are two translinear loops in it.
1) M20,M21,M22,M25 and also 2) M19,M23,M24, M26.
In quiesenct current calculation, the currents go through M19/M20 are equal. This tail-to-head coupling controls the minimum current of the output tansistor.