eqy:

By 4 losses, do you mean something like


Yes.



 eqy:

verify that the gradients should be different with lambda4 = 0.


Yes its different.
From your suggestion i start to observe the response of individual loss. Loss1 is GANLoss which is MSE loss and i check for only GANLoss with 150 training images as sample check. I observe that during start Generator Loss  and Discriminator Loss is in range of 1.6 and it quickly drop to range of 0.7 in second epoch and in range of 0.3 in third epoch. I run for 10 epochs but output image is not impressive. PSNR and SSIM during validation(just taken 4 images) is also fluctuating with wide range. Gradients at output image come in range of e-04 to e-05 from 1st epoch to 10th epoch.
Is the network is not converging or i need to check with more number of images?