Multisig question -- from a single XPRIV or XPUB (1/n), can the addresses be viewed? How about from a signing majority (m/n, where m < n) but not the full set (n)?

I'm trying to get a better handle on multisig for how Electrum manages it. I more or less understand how Bitcoin does it (I've read Andreas's "Mastering Bitcoin" anyway). I've read however that Electrum doesn't do multisig in the same way.

Say I have three people I want to inherit in the event of my death, but I don't want them to have access. Can I create a 4/5 multisig (keys ABCDE), pass one each of both XPUB and XPRIV (A, B, C) to the three people, and keep (D,E) for myself, while also giving both the XPUB and XPRIVs (DA, DB, DC) to multiple other parties (who are unknown to each other) for safekeeping and signing?

Would this allow the three heirs to look up public addresses in any way? Would this allow the other parties to sign transactions? Would the other parties only need the XPRIV/XPUB for their two keys, or would I have to give them the XPUBs for all five?

Thanks.