As Nanny J says, locating a church where two people married in Hastings in could be problematic (see Wikipedia: List of places of worship in Hastings.) Given that it is also presumed they were both reasonably mature and at least one had been widowed, the Registry Office seems more likely. Even if successful, you may find that rather than revealing the ages of these two adults and their fathers, a certificate may still side step the issue by just saying, "full age, father deceased."
Other than getting a copy of the certificate anyway through normal channels, perhaps you could ask the cemetery for more details, like if there are two buried in the same plot and if so, who is the other occupier and when did they arrive. Alternatively, you could try asking Hastings library to do a quick look up for the couple in a pre-war street directory, on an electoral role or an obituary in a local newspaper.
Roy G