I'm sure the three writers would have made more than Mick and John.
I'd say Stevie then Lindsey then Christine simply because Stevie and Lindsey have carried on making music and Christine has pretty much retired now.
As Macfan says a UK magazine had Christine's wealth estimated at £25,000,000. But I'm sure the article also said it was difficult to arrive at an accurate figure for people who spent much of their working lives abroad. so that figure might have under-estimated her true wealth.
Christine always strikes me as being very clever with money (after all the drink and drugs excesses were over) and I expect she gets very good advice.
I imagine she's comfortably off especially as each year the UK government gives all pensioners £200 towards their fuel costs and I expect she has a free bus pass
Gail