Questions regarding reusing an address

My understanding (not sure if I am correct) is that the risks are for privacy and (potentially) for the vulnerability to quantum computers that can break the elliptic curve digital signature algorithm. My questions regard this latter issue.

1) this vulnerability would lead to the uncovering of the private key. But are we talking of the master private key (the one derived from the 12/24 seed words) or of a lower level private key? I would think it must be the second case, otherwise after any spending transaction one would need to change the word seed. Am I correct?

2) Is a multi sugnature wallet more resistant to this problem or does it suffer from it equally?

Thank you to whoever may have the patience to clarify this to me!