Capital gains

Sadik Shaikh (ca) (52 Points)

16 August 2020  
Mr. A is a land owner. Makes an agreement with Mr. B ( land developers) that he will developed the land and all the developing expense shall be borne by Mr. B only and when the plot will be sale the sale proceeds shall se shared between Mr. B (17.5) and grandson and daughter of Mr A in ratio of 16.5 equally between 5 members.

Who will be liable for capital gain? Mr
. A his grandson / daughter?
When will capital gain arise when agreement is made between A and B or in the year when the sale proceeds will be receive after sale of plot?