Firstly, after looking at the "Funeral" advertisement, I think that the director chooses mixed race couple is because he or she wants to emphasize on racial and harmony between different races people. Even if the people are from differents races and religion, we still can become a sweet couple, and can communicate harmoniously.
Second, the director concentrates on bad traits is because that bad traits are always more memorable than good traits. But of course good traits are memorable. But the thing is, people tend to hate the bad traits when one person is alive, but after that person pass away, people will tend to miss the bad traits more than the good traits. Daniel's wife shows out how Daniel's snore is because even if she hate it previously, but she miss it now.
Thirdly, I think the advertisement is effective to promote family values. It entirely shows how does a mixed race couple communicate and loved each other, even thiugh they're from different races and religion. And also, it shows how precious it is to communicate with your family. You may not know what will happen if one of your family member pass away suddenly. It shows that we must cherish the good times now with our family, if not we may regret it in the future.