1. The real estate company owns the property right of the house and can sell (including mortgage) the house, that is, it has the initial disposal right of the house;
2. When he borrows money from you, he must use the house as collateral (not to sell it to you, you don't want his house), and you want him to pay back the money;
3. In order to guarantee your rights and interests, you must transfer the right to dispose of the house mortgaged by him and ensure that he cannot sell it privately;
4. The certificate of other rights is the proof of the right of disposition, indicating that the property right of the house belongs to him, but it has been mortgaged to you;
5. You have another right certificate, which can restrict him from selling the mortgaged property during the mortgage period (the Housing Authority has a mortgage record);
To sum up, the real estate company mortgaged the house to you and gave you his right certificate. Remember that his title certificate is in your name, so the real estate company cannot sell the house. Only when he pays off the money can he cancel the mortgage and other rights certificates, so that the house can be sold and your interests can be guaranteed.
A Bin, a real estate agent, will answer your questions.