Based on the situation of this couple, regardless of them being split soon after the winning, I think the best thing to do here is to cut the prize into half so that tensions between the two parties will de-escalate and avoid any confrontation or emotional turmoil and stress that sometimes end up so badly on both of them.
that's easier said than done because human nature is greedy and it is normal for them to be blinded by money and fight over it. if they think that each of them has full rights to the prize, then the best way to resolve this issue is to take the matter to court and let the court determine who is most entitled to the winnings. that's the only way to determine who has the most rights.