This is more than a remix. If these songs are to be released under the Queen + MJ name. Everything except the vocals and any piano pats Freddie may have recorded will be replaced.
Yet again assumptions are being made about the bussiness arangments and how BM and RT will or won't work. How do you know they won't work for a flat fee? You mentioned fifty percent of the money. What part of the money do you mean? The song royalties will go to the cataloged writer or writers of the songs. William Ordit will not be working on spec, he is a well known, name producer, so his fee and method of payment will have already been agreed, and if BM and RT are co producing, those arangments will have already been made.
If your talking about performer's payments it wouldn't be a 50/50 split, in this case it would be a three way split between Queen ( BM and RT ) and FM's estate and MJ's estate as they will all be featured on the recording.
But at the end of the day, the bulk of what these songs make, will go to Freddie and MF's estates and no one else.