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. Ego clash won't bear good results that is why we need to keep ourselves calm and fair with others especially in a situation like this.
Even friends disintegrates because of money tussle so it just very bad that some people have given so much value to money more than their relationship with others and if you enquire from this both couples their reasons for splitting you would find out that it may just be as a result of one among them trying to have a larger share of the amount being won.