My comment is really on two things; the references to a prenuptial agreement being drawn up for the split and also the complexities of sorting out their finances if they are splitting.
A prenuptial agreement is used before a marriage. I stress "before" and "marriage"! They are not married. It is used to set out what settlement there would be if the marriage ended and is being used more and more in the UK. They could have had a "living together agreement" which would be similar in some, but by no means all, ways. I suspect they have had drawn up (if the reports are true) a sort of hybrid "living together but maybe we won't be soon in which case..." agreement. Sensible too. Sort out the finances if you can to avoid the very high Court costs of a dispute.
Finally, given they are not married the legal position would be (if in UK) complex especially as they have 6 children between them and 3 of them are adopted. There would be issues of adoption law, parental responsibility and contact (a lot of people refer to this as "custody and access"), house ownership, the financial settlement, maintenance and housing needs for the children and so on.
But in the UK they certainly would not be "splitting their fortune" as in UK law a common law wife has no such rights and nor does a common law husband. A common divorce myth.
But let us not feel too sorry for them, at least financially. If reports are right they will now have to struggle with only $100million each. Tough life.