1) Joe has said his son will not be on any foreign boards if he is elected president. Again, there is nothing illegal about it if he did. Interestingly, it IS illegal in many other countries, but not here in the US. Is it a potential conflict of interest? Absolutely. Not illegal though. To avoid any possibility, Joe has said that Hunter will be prohibited from doing it and will therefore not have to bother with the scrutiny.
2) It was 50K per month, not 80. Not a particularly huge discrepancy, but these arguments always end up ballooning with the amount of money being made / profited.
3) Again, while you can claim that he is underqualified for the role, the doesn't mean that he didn't work in the company's best interests. If I understand correctly, he was serving as a liaison to European investors and he had served on previous boards in a similar capacity (acquiring investors). So is he an ideal candidate for this position? Meh. Is he better than hiring a clerk at the local 7/11? Absolutely. Again, it doesn't matter whether he is qualified or not. I've worked at family owned companies that employed some significant Nepotism. While some of those familial recipients were better at their job than others, I have yet to meet one that didn't at least try to do the job within the best of their ability. The same could be said for Ivanka. She is a freaking fashion designer, but is now working on multi-million dollar deals and trademarks with China. While I don't think she is qualified for that role, she is doing what is best for her company and is apparently succeeding. Kushner is a real estate guy. Not exactly the best person to send to the middle east to develop cease-fire strategies, but he is doing the best that he can.
4) I'd have to find the link, but I believe I saw that Hunter made no profit from the 1.5 billion investment. Yes it helped the company immensely, but it didn't help him personally (except for the obvious credit in being able to land the deal)
5) Trump's kids don't have to "join" any boards because they are already on the boards of a large multi-national business. There are several ways that their business has benefitted during their time in the white house. If you are actually open to learning about it, feel free to click on the link below. There is plenty there that could be considered corrupt, but a lot of it is mostly above board, just like the Hunter Biden situation. So I don't have a particular issue with what the Trump children are doing, just that is a bit hypocritical for them to be calling out Hunter Biden for similar practices.
https://www.gq.com/story/trump-kids-profit-presidency