Q1.
this question isn't clear. you mean something like this transaction:
https://www.blockchain.com/btc/tx/cce09841f35cf8f3a0f1f194746837a2d4dec15e7db469ba52d82c3d9deb4632there are different "senders" each having a different address (a different key) which they all are creating a single transaction.
if this is what you had in mind then it has nothing to do with multisig. it is a feature that existed for a long time, where you can spend multiple transaction outputs in one transaction and sign each of them with their respective private keys since they already are going to have a separate signature field inside the final tx.
Q2.
as far as i know, it is possible. because the way that bitcoin is using multisig is very primitive and easy to implement. basically you concatenate multiple public keys and then sign the tx multiple times and then concatenate those signatures together too. so as long as each of those altcoins support some sort of scripting language where you can tell the interpreter to "check_multisig" then they should be able to do it no matter what signature schemes they are using.
however, when we move to Schnorr and start using collective signatures when you just have 1 sig and 1 pubkey they won't be able to do it unless they are using Schnorr or any other DSA algo that allows safe signature aggregation.
