Two separate issues.
First, all Sonos speakers that are part of a ‘home’ can interconnect. There is always a 75 ms delay between a home theater ‘room’ and any grouped room, but this doesn’t apply when streaming music, only when the TV’s input is playing.
Second, Sonos doesn’t make a ‘home theater’ system for use in an outdoor environment. You can certainly take one of their soundbars outside, temporarily and use them, assuming there’s power available, but they aren’t designed for outside installation, you’ll probably want to look at the specs for each speaker.
You could conceivably use a Sonos Amp, connected to your TB via HDMI ARC, which would drive your choice of outdoor speakers. However, the best you can get is true 4.1, with the ‘interpolated’ center speaker created by your front speakers. The Sonos Amp is also not rated for outside use, but there are third party companies that make outdoor enclosures.
Speaking personally, I’m not a huge fan of outdoor Home Theater use by Sonos, there are just too many compromises that have to be made. None are insurmountable, given money, but you’re just not using the system as designed. It’s a hole in the Sonos system, IMHO, but I’m not sure there’s enough potential buyers out there to make it profitable for Sonos.
