A quarter of your password manager's password means it needs to be really long for it to not be bruteforceable if one or two quarters are recovered (on the order of at least 24 completely random alphanumeric characters)

Shamir's secret sharing scheme does not allow anyone to bruteforce it, no matter if they have 99 out of the 100 required pieces that unlock a 10-character password. If you want to do this sort of thing, I would recommend using a secret sharing scheme instead