Filtered Sales in Customer master without using relationship

Hi elemesey ,

I updated your sample pbix file(see the attachment), please check if that is what you want.

1. Delete the relationship between the table 'Fiscal Year based on Sales' and 'Sales'

2. Create two measures as below 

Measure = 
VAR _cust =
    SELECTEDVALUE ( 'Allcustomer'[Customer] )
VAR _fyears =
    ALLSELECTED ( 'Fiscal Year based on Sales'[Fiscal Year 2] )
VAR _fmonths =
    ALLSELECTED ( 'Fiscal Year based on Sales'[Fiscal Month] )
VAR _itemgroups =
    ALLSELECTED ( Sales[Item Group] )
VAR _dates =
    CALCULATETABLE (
        VALUES ( 'Fiscal Year based on Sales'[Date] ),
        FILTER (
            'Fiscal Year based on Sales',
            'Fiscal Year based on Sales'[Fiscal Year 2]
                IN _fyears
                    && 'Fiscal Year based on Sales'[Fiscal Month] IN _fmonths
        )
    )
RETURN
    CALCULATE (
        SUM ( 'Sales'[Sales] ),
        FILTER (
            ALLSELECTED ( 'Sales' ),
            'Sales'[Customer] = _cust
                && 'Sales'[Date]
                IN _dates
                    && 'Sales'[Item Group] IN _itemgroups
        )
    )

Sum of sales = SUMX(VALUES('Allcustomer'[Customer]),[Measure])

Best Regards