There are no restrictions on the locations you can use. It is perfectly fine to use all 12 stays (1 stay quota) at other subscription locations or other Co-Owners' locations. In addition to your own property, you can use all SANU 2nd Home locations.
Example of use: If you own one stay quota (12 stays), you can use 6 stays at your own property, 2 stays at Kawaguchiko, 2 stays at Ichinomiya, and 2 stays at Nasu 1st.