By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0. 3798917 fiddles created (41832 in the last week).
SELECT 01254601144 as UPC, 90 as TotalUnits, '2018-04-14' as Date
INTO #RTG_Lookup2_4_Ago
SELECT 01254601144 as UPC, 107 as TotalUnits, '2018-04-21' as Date
INTO #RTG_Lookup2_3_Ago
SELECT 01254601144 as UPC, 132 as TotalUnits, '2018-04-28' as Date
INTO #RTG_Lookup2_2_Ago
SELECT 01254601144 as UPC, 98 as TotalUnits, '2018-05-05' as Date
INTO #RTG_Lookup2_Last1
SELECT
MIN(Ago.TotalUnits) AS LowMvmt,
MAX(Ago.TotalUnits) AS HighMvmt
FROM (
SELECT * FROM #RTG_Lookup2_4_Ago
UNION
SELECT * FROM #RTG_Lookup2_3_Ago
UNION
SELECT * FROM #RTG_Lookup2_2_Ago
UNION
SELECT * FROM #RTG_Lookup2_Last1
) AS Ago