Column A      Column B        Column C
date          amount          category

=ABS(sumif(SHEET1!C2:C, "Widgets", SHEET1!B2:B)+sumif(SHEET2!C2:C, "Widgets", SHEET2!B2:B)+sumif(SHEET3!C2:C, "Widgets", SHEET3!B2:B))

=FILTER(B:B, A:A>=G1, A:A<=G2, C:C="Widgets")

=SUM(FILTER(B:B, A:A>=G1, A:A<=G2, C:C="Widgets"))

=sumifs(Sheet1!B:B,Sheet1!C:C,A3,Sheet1!A:A,">="&A$1,Sheet1!A:A,"<="&A$2)+sumifs(Sheet2!B:B,Sheet2!C:C,A3,Sheet2!A:A,">="&A$1,Sheet2!A:A,"<="&A$2)+sumifs(Sheet3!B:B,Sheet3!C:C,A3,Sheet3!A:A,">="&A$1,Sheet3!A:A,"<="&A$2)