You and another person had sent in asks about this, but the other user's asks disappeared from my inbox before I could answer them D: A shame because they'd included a cute and funny piece of art of a gijinka MK drinking out of an absolutely massive teacup.
I came up with a sort of non-answer to both asks, because I don't drink tea myself and can't say with much confidence how they work, but if I did I would probably assign them teas based on these vibes (the poofed ask inquired about these three):
MK: something mildly sweet/floral with complex flavour. He likes the layers to the taste, and not too sweet to begin with so he can add sweeteners to it depending on his mood.
Vul: something bitter and strong, just to say he does, and on the blander side, but is also guilty of adding lots of syrups and sweeteners to it. He can drink it straight though if so inclined, and has brewing it down to an art.
Kirby: pretty much anything! Maybe the most bitter of bitter teas will make him a bit reluctant, but he will drink whatever you give him. He's not picky :)
And have this silliness that the giant teacup art inspired, I may have lost the source prompt but I wanted to share it anyway: