If a photographer is "commissioned" to take the photographs "for valuable consideration", then copyright resides with the person(s) commissioning the photo (according to Copyright Act). IP Office of Singapore further states that if a photographer is "engaged" by a person to take his/her photo, then copyright resides with the person (not the photographer).
All this is of course modifiable by agreement/contract.
So unless explicitly assigned copyright by the couple, the photographer does not own the copyright. As a middle ground, perhaps consider having the agreement/contract assign rights of
reproduction to the photographer, without further payment or royalties, for use in the photographer's portfolio and/or other purposes, commercial and non-commercial.
Some folks are very honoured to be "published", some consider it an invasion of privacy. Even with your legal rights covered, always ask, to save yourself the ill-will and potential "bad press".