Using MultiSig

There are client libraries, such as https://github.com/XRPLF/xrpl4j (in Java), that make it easier to use multisig.

This example creates a multi-signed transaction and submits it: https://github.com/XRPLF/xrpl4j/blob/main/xrpl4j-integration-tests/src/test/java/org/xrpl/xrpl4j/tests/SubmitMultisignedIT.java#L139

You can collect signatures separately and then assemble them when you have enough to submit. To do this, construct a MultiSignedTransaction, then call xrplClient.submitMultisigned.