From the LT8602 datasheet, pag. 19, I saw that the output capacitor should be: Cout>10*L*(Ilim/Vout)^2.
For channel 3 and 4, is the Ilim(TYP) = 3.1A? (In the datasheet pg. 4-5 I saw SWx Average current limit between 1.8-3.5A).
If so, with Vout=1V (for channel #4) and L=1.5uH, Cout should be: Cout>144uF. Is it correct?
The equation is right, and it is for 5% overshoot. If you do not need such small overshoot, the cap can be smaller. Also a 1uH or smaller inductor is usually good for 1V output. The schematic in the datasheet gives reasonable values, and provides a start point for your real applications.