this is from December 2013

http://news.tokunation.com/2013/12/2...n-3-2015-13663

But apparently, the negotioations didn't go well, as the statement tweeted by Yoshi is the most recent info on the matter.

Do all the sentai shows take place in the same universe or is each sentai series its' own universe? The only sentai shows I've watched are the first 10 or so episodes of Gokaiger and Akibaranger. So I'm asking because I don't know.

Sentai tend to be their own separate entities. There are crossovers between the two most recent, but only Gokai treats them as one solid universe. Every other series operates alone.

Though Gaoranger did bring together several previous rangers. So you can argue in that case it was one big universe. Same goes with Super Sentai World.

Not really, as you can say that Sentai as a whole is one big universe due to the various crossover movies.
But because references are sparse and they don't operate beyond those movies and specials, it's hard to call it one big universe.

Denjiman and Sun Vulcan do canonically take place in the same universe though. The main villain from Denjiman is revived in Sun Vulcan to fight the new team. She even mentions having fought the Denjiman before when she first hears about Sun Vulcan. We didn't have any other in-show reference like that outside of Gokaiger, but that could be an argument to consider the whole franchise as one big universe.

What if we have a main robot could have a second sword ?

We did, it was called GokaiOh.

And before that it was DaiBouken if you want to count a pickaxe and shovel as "swords." Plus Kyoryujin had Dricera's drill tail which in practice could be seen as a sort of second sword.

And while it wasn't a main robo, OhBlocker had two swords.

If we have a truck mecha ?