Yhwach has no capability to truly care for other people. He operates on the basis that all relationships are strictly beneficial or they aren’t worth having. He views the lives of his close comrades as fodder to be used whenever it benefits him more than their continued lives.
While Madara is a jaded, depressed and maybe even bitter old man, I do not think he would find Yhwach appealing at all. As a person, you are basically dealing with ego incarnate.
“everything in the world belongs to me to steal” —Yhwach only slight paraphrased.
Madara may be a hypocrite—wanting peace but craving war—I do not think he would be capable of accepting Yhwach’s detached view of life.
Imu seems like the middle man between them. He has the audacity to declare he owns the world, to claim people like Harald’s lives benefit him more than Harald’s own family members. But he’s also not a total psycho and seems based in a very brutal philosophy of might makes right. Something Madara understands & holds some resentment towards.
in short; Nobody is getting along, Yhwach is too much of an abnormal monster. Imu’s ego and self importance wouldn’t allow for anything close to friendship to form with Madara who would probably see Imu as technically correct but lacking.