For many people, household labor remains demanding even if able to afford household appliances their grandparents would find a miracle.
Option Elimination -
First, let us understand the usage of "would find" and "would have found" that is key between options C and D.
"would find" construction is used for hypothetical or conditional actions in the present or future. It introduces an unlikely scenario. E.g., If I had more free time, I would find time to read every day. It means I am presenting an unlikely case that " It is unlikely I have or will find time." But if I do, "I would find time to read every day."
"would have found" construction is used to express a hypothetical action in the past. Action or situation that never really happened in the past. We think about the past and think about the outcome. E.g., If he had attended the concert, he would have found the performance outstanding. This never really happened in the past. Not if he goes in the past and supposedly attended the concert, "he would have found the performance outstanding."
(A) even if able to afford household appliances their grandparents would find a miracle - who can afford them? Need "they." Moreover, "would find" is used for hypothetical actions in the present or future. So here, it conveys an ongoing or present reaction from grandparents. However, in the context of the sentence, we are talking about grandparents, so it's better to use the hypothetical in the past.
(B) despite being able to afford household appliances their grandparents would find a miracle - "would have found" is better to convey the hypothetical action in the past.
(C) even if they can afford household appliances their grandparents would have found miraculous - perfect.
(D) although they could afford household appliances their grandparents would find miraculous - "would have found" is better to convey the hypothetical action in the past.
(E) even if they are able to afford household appliances which would have been a miracle to their grandparents - "they can afford" is a better usage. Moreover, "which would have been a miracle to their grandparents" adds unnecessary complexity.