Check if the value from one table exists in another tables in SQL Server
I think you could get it with a single statement.

CREATE TRIGGER t1_insert ON T1
AFTER INSERT
AS
BEGIN

    IF EXISTS(SELECT 
                  1
              FROM
                  inserted
              JOIN
                  (
                   SELECT ID FROM T2
                   UNION ALL
                   SELECT ID FROM T3
                   UNION ALL
                   SELECT ID FROM T4
                  ) others
                  ON others.ID = inserted.ID)
    BEGIN
        PRINT 'YES';
    END
    ELSE
    BEGIN
        PRINT 'NO';
    END

END


db&lt;>fiddle here