1) I like
Isla Angelica. Congrats to them! :)
1) I love
Jacob.
Jakob is okay too because it's the traditional
German spelling and used to be very common as a middle name in my family (usually after
Johann), but I highly dislike
Jakub (that spelling doesn't really sit well in English-speaking countries). Anyway, I think it's okay as a first or middle name. Jacob/Jakob
Isaac Walter is a nice combo.
3) I like all of the combos you have presented, but I wouldn't use
Jakob Astor unless you're okay with people asking if he's named after
John Jacob Astor IV, who died on the Titanic. Anyway, I love
Persephone Violet!