First of all, a large private house can be transferred to your mother under legal procedures if it is your father's legal personal property and has relevant property certificates. The specific operation requires you to consult the local housing management department for relevant procedures and materials.
Secondly, if the small house is a public house and your father is the legal tenant or property owner of the house, then you can consider transferring the house to your grandson. However, it should be noted that the relevant regulations in different cities and regions may be different, and it involves the transfer of public housing property rights, which needs to be operated in accordance with relevant legal procedures and regulations. At the same time, it is also necessary to find out whether the property right certificate of the house is lost. If the certificate is lost, you may need to go through relevant procedures.
Finally, whether the house can be transferred before the demolition needs to take into account the local urban planning and land management regulations. If the relevant regulations allow the transfer before the demolition, then the relevant operations can be carried out under legal procedures. However, it should be noted that the transfer of housing property rights must comply with relevant legal procedures and regulations, otherwise it may involve property rights disputes. It is recommended that you consult the local housing management and land management departments to understand the relevant regulations and procedures before any operation.