pivot with primary axis 2 tables as input and secondary axis the same unit?

Hello,

this is my first time on this forum, I hope this works out with the question I am introducing.

I have the following situation where I visually want to report tracking of in and outs on projects.
2 (or multiple) tabs or used at this point.
On each tab I have a table (wich are individually defined as tables)
for example: tab 1 Input with tblInput, tab 2 with tblOutput, tab 3 with tblBaseData

The setup I have now is:
1. tblBaseData has the main product data reference and is linked to tblInput and tblOutput so that there are links between the tables. (one-to-many relation)
2. tblInput has a date column for amount and release date
3. tblOutput has a date column for amount and release date
What I want to do is use a pivot diagram to see the difference in In and Output in time (I do not know the term in English, stagnating or summate value in time)
the issue I am running into is that the X-axis is the time axis and both tables have different dates included but I want to stick with one main axis (for example months).
The Y-axis stays the same as being the amount.

Could someone help me how I can solve this?
Maybe a different approach is better; I am open to hear about this.

Thanks in advance for your willingness to read this and to your answer.

Regards, Johan