the message : “The aggregation cannot be applied to a field”. is saying that you can’t do that ‘math’ on this type of data. and if you are collecting this data in a TEXT field this could be part of your problem. if you need to do things like ‘sum’ then you need to work on numerical fields as a rule.
As to the filtering, yes, the filter selector can only be set to one data source, and where here, you have 3 different datasources, it won’t do what you need. Have a look though at the options in how you can use the SetFilter behaviour under a button on your report perhaps (you can have 3 seperate SetFilter actions to each of your datasources for instance) and where (if working on numerical or date fields) can set filters to show specific ranges of dates. You can also then use the ClearFilter behaviour to reset filters before applying any new filtering as well if required