The idea that veganism is cultural appropriation is just silly. Eshe Kiama Zuri comes out of this badly, and they appear to be a divisive, overly woke troublemaker who doesn't know that in your 20s you are not as wise as you think. That being said, they make some serious allegations and there may well be some problems that need to be addressed. I wouldn't be surprised if there is at least some credible issue there, even if they are exaggerating it.
It's very hard to tell who is really in the right unless a lot of other people comment, or a credible outside investigation is made. It may be worth paying for an outside investigation and report, which I imagine would cost of the order of £10,000 which might be worthwhile.
There are both specific allegations like the claim that the N-word was used in conversation, as well as the general point that veganism is a somewhat white movement. This could be addressed by taking specific actions to get more people into the organization using targeted advertising, headhunting, community outreach.
On the question of BDS, I think it makes sense to hold back a notch from the organization formally supporting BDS, which has very little to do with the society's goals and would unfairly alienate Israeli vegans. I think they should put out a statement saying they support the struggle of the Palestinian people including some modest financial support for animal rights there, that they don't generally buy any products or services from Israel, that some of their members personally boycott Israel as individuals but they don't feel a formal, full boycott from the whole society is appropriate.
On the question of the Daily Mail: remember one of the functions of the Daily Mail is to provide support for its readers resistance to change. The purpose of this article is to help its readers feel less guilty about eating meat by thinking "these loonies at the vegan society are mad, therefore their arguments about veganism are mad, therefore I can continue to eat meat guilt free."