When you visit each of the subdomain’s sites, the Issue to: will just be domain.com. How can I have it show its full domain as in sub1.domain.comsub2.domain.comsub3.domain.com
If you want the common name to show your subdomain, instead of the first domain in the domain list, you should request a certificate for every one of the subdomains.
There can only be one “issued to” while there can be hundreds of names in a SAN.
Unless the site throws a validation error. no one looks at the “issued to” field.