They're fake marriages Hoppy. It's all really just another soap opera. I must admit I watched some of it, because it is a bit addictive, but not watching this series. I think Harry and Megans netflix filming is much the same - Nothing real about it!
They can't be legal marriages because in Australia the bride and groom have to give 'notice of intended marriage' at least one month before the ceremony.
They Us version of the show does have legal marriages.