What should I do if I want to get rid of a person's name in the real estate purchased by my brother and sister in Chengdu?

You can't go through the formalities of adding a name to an unknown mortgage, and you must cancel the mortgage registration first, but you can rest assured that the division of repayment rate of an unnamed mortgage after marriage is the same as yours. If divorced, you can get 50% repayment rate and 50% property appreciation. So your loss won't be too great, and the down payment won't count as you at most.