You can find a lot of Marshall Rosenberg lectures and even full workshops on YouTube.

An important part of the nvc practice is to give up attachment to outcome. Making a true request means that there will be no negative consequences if the answer is “No”. It is possible that your wife’s brother was triggered partly because you insisted (if you did), maybe he needed autonomy, solitude, to feel that he matters, to grieve, to rest.

I teach NVC and often use a small yellow book called Communication Fundamentals by Jean Morrison.