Business gifts: who counts as a business relation?

Everything you describe seems perfectly acceptable to me.

One of the conditions for claiming expenses is that the expense must help your business move forward. That's super vague, of course, but I think it often boils down to the story you have to tell, right?

So if you've had a good working relationship with a fellow self-employed person and you want to reward them with a gift, I think that's fine for your accounts. Because you will probably be able to work together even more in the future, build a closer bond, a lasting relationship... That's the story, of course ;)

Business gifts are actually "only" 50% deductible. There are exceptions to the rule that allow this to be 100%.
This uRL states it nicely. I had the same question and found their explanation quite clear: https://www.sbb.be/nl/magazine/relatiegeschenken-fiscaal-aftrekken-50-helemaal

As for who you can give this to: the situations you describe are definitely applicable :)