Use one node.js with multiple domains and certificates

Question

I have a system with API using node.js. Usually I configure it to use SSL with the help of PFX file and a password, or certificae PEM and a key file pair. The question is if I can use the same configuration in case of multiple domains (not subdomains of one upper domain), each one having separate SSL certificate (with same root), and how I can do it (combine certs and keys in one PEM?).

Thank you!

I exported all certs and unencrypted keys into separate files, don't know how to combine it all in one PEM.