If I recall, in some of the tips, they’ve stated that Voyager Witches like Bern and Lambda are witches with no personal ties to anything, and thus can roam freely between boards/worlds. Featherine is a Creator witch, which is stated to be somewhat on the level of a god due to the fact that they create from nothing, and are thus above Voyagers (if Maria in Fantasy honed her skill to be the Witch of Origins, she could one day rise to the rank of Creator). And then I guess there are the lower ranked witches who have powers only on their particular game board, although with things past EP6, it gets tricky since EVA and Ange can use their magic outside of the game board they’re connected to.
With Beato, though, it’s easier to explain. She has total power over her dominion, which is October 4th to the 6th of 1986 on Rokkenjima. She exists as a witch prior to it, but her game board is that of that particular time and place, so she’s at her strongest during that timeframe, and her power seems to be tied to her being on the board. She can roam almost freely across the board and mess with the pieces, but cannot change it to say, Hinamizawa in 1983 with the Stardust Crusaders cast instead of what she has, and nobody else who has control of her game board past that cannot change it completely, but can play the game in a way she wouldn’t.
And as for witches of the future, aka EVA and Ange, they are considered stronger than say Beato or Virgilia or even Bern, because the future, unless they choose to not have a future, has numerous possibilities for them (at least, I believe that is why they’re powerful. It’s been a while since I last looked at EP8) and the past witches are set in atone in which they no longer become relevant?
As for how witches are made… I believe it’s implied or outright stated that for all of them except for Featherine and Virgilia, witches are born out of hardship, suffering, and enduring. They are a desire to escape an ordinary life and are rewarded with magic for their suffering. Or, girl suffers, uses magic, becomes witch, being Majo is suffering. (It’s a lot more complicated than that and doesn’t explain how they become aspects.)
Feel free to elaborate on what I have missed or interpreted wrong, I love the witch aspect of Umineko and would have loved for it to be elaborated on.