How to use three query as a subquery?
you can do it this way:
;WITH FirstQuery  AS (
    SELECT SUM(QTY) AS QTY, SUM(IWeight) AS Weight, EntryDate
    FROM     ConIssuance
    where EntryDate between @FirstDOM and @LastDOM 
    GROUP BY EntryDate
    order by EntryDate asc
)
,SecondQuery AS (
    SELECT SUM(s.prdqty) AS qty, SUM(i.weight) AS Expr1, s.EntryDate
    FROM     Probale AS s INNER JOIN
                      ItemMasterFile AS i ON i.CodeItem = s.Codeitem
                      where S.EntryDate between @FirstDOM and @LastDOM 
    GROUP BY s.EntryDate
)
,ThirdQuery AS (
    SELECT SUM(Bweight) AS weight, SUM(Bpqty) AS qty, EntryDate
    FROM     Bigbalprd
     where EntryDate between @FirstDOM and @LastDOM 
    GROUP BY EntryDate
)
SELECT *
FROM FirstQuery
JOIN SecondQuery ON SecondQuery.EntryDate = FirstQuery.EntryDate
JOIN ThirdQuery ON ThirdQuery.EntryDate = FirstQuery.EntryDate;

If you have gaps (no records for some dates in some of three tables) you may need to use FULL JOIN with a bit more complex join conditions or even generate a list of dates (in case if you need a row for each date even when data for this date is not presented in any of your tables)