Do we allow a buyer of our property to withdraw EPF to pay the 10% downpayment ?
Will bank loan be approved upon the S&P agreement is signed ?

For the second question :
Bank loan and s&p are two different thing, unrelated to each other. Some people sign the s&p first, then apply the loan (can be dangerous if the loan suddently rejected), some people wait for loan approval first before signing the s&p.

What documents needed for bank loan usually ?
What happen if bank loan approve and don't sign the S&P ?

Nothing will happen if you not sign for the loan. Bank wouldn't charge you anythings.
So the more safety way is to look for a property first, place some deposit (better to state that if the loan not approve,you can get back all or some of the deposite.Depend on your agreement with the seller.),then get the loan approved first then the last thing sign the S&P.

The doc need to apply loan.
Photocopy IC
Salary Slip 3 to 6 months
EPF statement
Bank statement (your saving account)
Income tax
Business registration form. (If self employed)
Business bank account
Booking reciept for the property.

That means the seller must depend on the buyer to get loan before S&P can be signed ?