The light at sunset is going to be all over the place, you dont really want to even it out too much, really concentrate in making the couple look ok, as they ate the ones you are lighting. The key things are the softness snd illuminance. Set exp comp or meter to be +2 on a white dress. Set your ct for flash, or if you use mods set it off a grey card with mods on.
Shoot Raw. Tweak.
The sun is behind the couple, so unless you shoot with then totally crunched black ANYTHING will look unnatural.
Might as well only shoot with an effective 43mm lens with the subject always dead centre and printed at life size, because like fill flash at sunset, anything else is unnatural.
I jest of course.
Ct your subject for the light they are exposed with.
The ambient ct changes by the second at dusk, so don't worry about it. The couple are important. The absolute accuracy of the sky behind, not so much.