How get the sum of two tables value using inner join
This may not be the best way to do this but it will work.

SELECT c.ClientNo, c.ClientId, c.FullName, i.InvoiceTotalDue, i.InvoiceTotalBalance, r.ReturnChequeTotalDue, r.ReturnChequeTotalBalance, (i.InvoiceTotalBalance + r.ReturnChequeTotalBalance) AS TotalBalance
FROM Client_TBL c
LEFT JOIN (
SELECT ClientNo, SUM(TotalDue) AS InvoiceTotalDue, SUM(TotalBalance) AS InvoiceTotalBalance
FROM Invoice_TBL
GROUP BY ClientNo
) AS i ON c.ClientNo = i.ClientNo
LEFT JOIN (
SELECT ClientNo, SUM(TotalDue) AS ReturnChequeTotalDue, SUM(TotalBalance) AS ReturnChequeTotalBalance
FROM ReturnCheque_TBL
GROUP BY ClientNo
) AS r ON c.ClientNo = r.ClientNo


And of course you could change the subqueries into CTEs.  But basically you are going to collect the data pre join since otherwise you are probably going to get bad data (Client 2 for example will have Invoice info that is twice as large and ReturnCheque that is 3 times as large.)