I don’t believe you can use the certbot internals like this. The
acme module is lower level and assumes you will keep track of the certificates yourself and doesn’t offer you access to Certbot certificates.
Unfortunately I’m not an experienced Python developer or a Certbot developer. Maybe someone more versed in either of those subjects will be able to offer further advice. Given the two options on the table in your shoes I would probably accept the burden of having to manage more of the certificate lifecycle/storage with my own code & the
acme module rather than shell out to Certbot from a web application.