How can I stream (Jackbox) with the lowest latency possible?

For what it's worth, my personal experience was that Hitbox has far less stream delay than Twitch, which was why I preferred it over the more popular site. Something closer to 5-7 seconds was the norm, from what I recall. I haven't personally tried Steam Broadcasting in any significant amount, so I'm not sure how it compares.

(Just in case, disclaimer: I have no affiliation with any streaming service, other than using Hitbox on the rare occasions that I stream.)

Unless you're planning on allowing people other than your group of friends to watch the game, any group video chat or screen sharing software would be perfect for your needs.

Google Hangouts have incredibly low latency (< 1 second in my experience) and allow you to share your screen with others in the chat. Google Hangouts are also free if you already have a Google account. I've personally used Google Hangouts for this purpose, and many other times I've had to share my screen / look at someone else's screen. While there are some quirks if you also speak through the Hangout, this shouldn't be a problem for you if you're using Teamspeak.

As another option, join.me is a screen-sharing alternative that is free, lightweight, and easy to configure.

There is a new streaming service over at https://mixer.com/ which offers almost instant streaming (roughly 500ms in the worst case scenario) when using their FTL protocol. As long as your friends use a HTML5 compatible browser they'll see what you see with little to no visible latency. FTL will be rolling out to everyone over the next month or two by the sounds of it. Streaming on their service without using FTL is also quick, however. Last time I checked it had less latency than that of Hitbox and Twitch providing your network speed supports at least 2000kbps upload and your streaming software's settings are correct.

You can watch their blog at https://blog.mixer.com/ for announcements as to when they launch FTL to the whole userbase.