It can be doable could you please attach the workbook by replicating same scenario with superstore data
because without your field arrangement it would be difficult to write a calculations to achieve the Output
Also, what is your criteria for "top", is it the total, or the average, or the last month in the selection ?
Criteria I used is Table Calculation Percent of Total.
And used Index() function to show only Top5 based on Current month.
And anyway we can exclude the brands which is not continuous.