do will = pay rm10 stamp duty

pro of doing will = save stamp duty
con of doing will = other children may contest the will if excluded from the will, but in this case if that child is solely paying the house instalment, even if contested that child servicing instalment high chance to get the property since he's paying the instalment. but this doesn't mean the other children will initiate legal proceeding and all parties will be stuck for 1/2 - 1 year to battle it out.

transfer now = pay 50% stamp duty

pro of transfer now = that child con9lan7firm will get the property, but need to refinance the loan
con of transfer now = pay higher stamp duty + need to refinance loan (might be diff interest rate)

so, best to decide based on the circumstances.