I think something to consider re: suiciding familiar is that Baldur isn’t exactly a normal animal even by those standards. Even if it’s manifesting as an owl now, we’re talking about A) The personification of a vaguely magical sword, or B) Something conjured wholly from the mind of a delusional aasimar paladin. Either way, if it still considers itself a weapon to be used in battle, I think there’s a case to be made that Baldur still sees the poisoning idea as the kind of thing he’s meant to be doing.
Or I’m reading way too much into it, but that’s nothing new .