50:50 will still be the starting point despite the disparity in earnings, yes - the basic view (which of course has lots of 'ifs and buts', caveats etc.) is that a marriage is a partnership and everything within it is shared, the lesser earning partner usually has contributed more in other ways such as doing the lion's share of the raising of children, but even if not and one party earns much less purely through ill-fortune, ill-health or is just lazy or a gold-digger or whatever, that's the choice of both parties to be in a marriage with that financial disparity... that being said if it came to court as opposed to them agreeing between themselves, the judge would look at the entirety of their circumstances to come up with a fair split which could end up being different to 50:50 in either party's favour, so it's very hard to say without more details on their exact financials e.g. value of their home, value of other assets, income of both parties, house-prices and cost of living in the part of the country they live in. For instance it's possible if some of the assets were the DH's before the marriage he could be allowed to keep them rather than sharing, but in a long marriage probably unlikely.
They will also need to look at both their housing needs, particularly as they have 2 children and are looking at joint custody, so they both need suitable accommodation to house the children on 'their' time - if the wife doesn't earn a high salary she may not be able to get a large mortgage for instance, so may need more capital to fund purchase of a suitable property, or there could be an order for her to keep the former marital home, possibly with him continuing to contribute, and then it to be sold once the DC are grown and proceeds split at that point - but then again he will also need to house himself suitably too so in for instance a scenario where there is a very large/luxurious family home that takes up nearly all the parties' capital, the order could be it needs to be sold now and equity split so both parties can buy a smaller 2-3 bed house to house themselves and children. Don't forget both their pension funds are notionally in the 'pot' too so if his is much higher than hers due to higher earning, he could possibly have to give her slightly more of the cash assets such as equity in the house or savings to compensate.
Divorce is an expensive old business unfortunately and whether you're a billionaire or on the breadline, the usual outcome is both parties end up feeling financially hard done by and living a less nice lifestyle than before, it's kind of inevitable when you go from sharing everything to having to fund 2 separate lives 
.
That being said, the parties should absolutely both take individual legal advice and try and sort out a fair settlement without having to resort to court which will both save them money and a fair amount of hassle and stress, helps keep things amicable too which is a very good thing for the DC if nothing else!