How to Sum Variable Columns and Rows Using VBA

Good afternoon - I am attempting to create a spreadsheet that will have 4 different summation columns to it. The amount of columns between the four main will vary depending on the amount of tabs in the workbook. The four main columns will be summing information from the feeder columns that are fed from the individual tabs in the workbook. For instance, there are Three tabs to the workbook that flow to the summary tab. The information from each tab is gathered to the appropriate columns (12 different columns used for this) and then the information is summed across 4 different times in the main columns labeled "3 months ended", "6 months ended", "9 months ended", and "12 months ended." However, if I add another tab and now have four tabs, I need the summation to still be in the main four columns and include the additional tab as four new columns. So, it should be something like this (f = feeder column; M = main column)

Original:
f f f M f f f M f f f M f f f M

Updated with additional column:
f f f f M f f f f M f f f f M f f f f M

I apologize if this is confusing, I am brand new to VBA but I think it is the only way to do what I need the spreadsheet to do.

Thank you so much!!!!