How many forms 26QB to be filled?

so for 10 installments...I have to fill 3 forms? all total 2 buyers and 1 seller

for a joint buyer...how many forms to be filled for each transaction?

Let me take an example

Installment 1 - Paid 5 lakhs to the seller (TDS becomes Rs 5000)

Buyer 1 to fill Form 26QB and deposit TDS Rs 2500 for Installment 1
Buyer 2 to fill Form 26QB and deposit TDS Rs 2500 for Installment 1

Am I right?

Thanks everyone for your answers. But I am going to ask few more questions to clarify more:

Under-Construction Property Purchased: 2016 Jan
Installments Paid: 9
Installment Due: 1
TDS Deducted by Seller: No
TDS Deposited by me: No
Possession: to be taken this month

If I want to pay TDS today:

1> I have to submit 20 Forms 26QB for 10 installments?
2> Will there be any penalty?