Please help us to help you by reading and following the posting guidelines located in this thread: Please read before requesting assistance. The more information you give us the better we will be able to assist you. Thank you.
Environment details?
Version of osTicket?
Two instances means two configured web sites, two sets of code, and two databases (or one database with separate prefix w/ credentials. I do not know if there is a way to do all that with a Synology DSM and this sounds like a question for them. Keep in mind that your ram and storage usage will vary wildy based on the size of the ticket systems, your php configuration, and server load.