How to get necessary Fields for Report from 3 Datasources

Hi everyone,

I have Question regarding combinging 2 or more Datasource. i have read some article on Internet but not fully understand, so i want to ask you

Suppose i want to create a Report like this

For Field 1 and Field 2: i found these Fields in Standard Data Source1

For Field 3: i found this Field in Standard Data Source 2

For Field 4: i found this Field in Standard Data Source 3

Suppose i  activated and replicated these Datasources in BWs, and i have installed relevant Info objects.

So my question are:

1. How can i join 3 Datasources to get 4 fields for my Report above?

2. Do we need to create 3 Cubes for 3 DataSources and then create a Infoprovider?

3. How to check if 3 Datasources be linked to each other? i mean which T-code can we use to check the Relationship among Datasources?

Thanks!