I use VSDC - both free and paid versions - easy to add sound tracks - here is a
Link to their web.
Also the photography/video market for real estate is an extremely competitive market. Many agencies have photographers they used for a long time. I would check face to face (of course staying 6 feet apart ? ) to see what your client wants and expects.
Are you already a photographer that is adding drone services to your already established business ? How much experience do you have doing real estate still photos ?
Do you have your Part 107, which you will need to legally pursue that line of work, are you carrying insurance, etc ?
These are the type of questions you will need to be able to answer to the satisfaction of new customers.
CommercialDronePilots has one section covering real estate
Good luck