Automatic breakdown of hours into columns

ok so I used this formula (see my previous comment, I've not noticed we changed to "ISNUMBER" test)

=IF($Position1 = "SS", IF(AND(ISNUMBER($[SS Hours]1), ISDATE($[Start Date]1), ISNUMBER($[Duration (months)]1), [Apr-20]$6 < $[End Date]1, [Apr-20]$6 >= $[Start Date]1), $[SS Hours]1 / $[Duration (months)]1, ""), IF($Position1 = "MO", IF(AND(ISNUMBER($[MO Hours]1), ISDATE($[Start Date]1), ISNUMBER($[Duration (months)]1), [Apr-20]$6 < $[End Date]1, [Apr-20]$6 >= $[Start Date]1), $[MO Hours]1 / $[Duration (months)]1, ""), ""))

and it still comes back as invalid operation. Should we add something else somewhere? Or am I missing properly closed condition (parentheses) somewhere?

Yes, [Apr-20] onwards are all text/number formatted as I need numerical value there

@Paul Newcome I am not sure if this helps, but I provide a sample with the formulas in excel that work. Please note lots of columns are hidden in the sheet, however, my intention is to apply the formula for the incoming projects, not the past ones.

Hopefully you'll get the idea of what I'm trying to achieve :) The data in [Apr-20] onwards should show average hours per month, my idea is to put the formula in my whole row so it autopopulates as in the excel sample I provided ( you can try to just change the hours, start date or duration and the numbers automatically change).

Is this what you mean?

I have a mock sheet where I'm just entering values in SS or MO to get us sorted :)

The [Apr-20] as well aas all columns onwards are formatted as number/text:

There is currently a numerical value in them inputted manually.

@Paul Newcome that's the thing, I am not trying to input a date into the [Apr-20] column or the ones afterwards. My intention is to have a numerical value there. So if I have a project that runs from 01 April 2020 to 31 March 2021 (12 months) and my budgeted hours in total for the project are 120, then I would like to have the [Apr-20] [May-20].....[March 21] to be automatically populated with number 10. So I would like the [Apr-20] etc column to have formulas there, so when I get a new project, I only enter the date, duration and budgeted hours, and the rest of the columns [Apr-20] etc will populate with a value obtained by division of budgeted hours/duration.

So I do not have to manually go into respective columns and drag fill them for the duration of the study, but that it will automatically calculate and populate, like in the sample Excel sheet I shared here:

Is there any way this would be possible??