For direct synchronization between Thunderbird/Lightning and Android on your local network, you could also try GeneralSync, which is free (as in beer) during the open beta that started yesterday. As its main intention is to provide an easy and safe decentral sync for end users, it does not open ports by default, so you need to manually set up NAT and hostnames if you wish to use it via Internet.
Disclaimer: I’m the developer of GeneralSync (and only posting as this thread seems to be more about Thunderbird / Android calendar sync than about Syncthing).