Both Longjiang satellites carry a VHF/UHF amateur radio transceiver built and operated by the Harbin Institute of Technology in China. They've open sourced software specifically so radio amateurs can decode telemetry as well as image data: https://github.com/bg2bhc/gr-dslwp
Depends on the wishes of the people who originated the signal. There are plenty of OTA signals that are free to the public, like NOAA weather satellite data. They're paid for by the public and are in the public domain. I don't know specifically about these signals, but it seems like the Chinese government is pretty open with them as well.