I'll toss my two cents into the mix, as I've an affinity for doubles (Gives you someone to berate in the final stages of a race...), and have owned a few. To date, I've owned both the fg and carbon versions of the XT double, the Stellar Excel Double, and the Fenn Elite in carbon. Currently own the XT carbon and the Elite carbon.
Generally, the double versions of the venerable single boats are noticeably more stable than their 'tea for one' counterparts. I guarantee that someone who swims in an Elite single will stay upright in an Elite double, twitchiness aside. For all around use, it's hard to beat the XT-it has a good turn of speed, and aside from the double rear footwells, and their flexy rear footplates (not so the front one), it's a great boat and loads of fun. The Elite is a bit more 'caffeinated.' It is faster than the XT on flat water, and in the hands of skilled paddlers. Midpackers will likely find themselves faster and more comfortable in conditions in the XT. That said, the Elite is surprising stable for a boat wearing that moniker. The Stellar is in between the two in the mix. It has almost the speed of the Elite, and more stability, but is fairly low volume, hence lighter paddlers will be better off in this boat.
As a doubles paddler (and a mountain tandem cyclist amongst my other hats), the difference in acceleration takes some getting used to-the doubles feel a tad mired when it comes to a quick jump. Likewise, the timing takes some getting used to when dropping in on a run-you accelerate the same way you do on a single ski, only to find your stoker in the rear is yelling at you, because they're chest deep in the wave that just washed over them. Oops. Once firmly on a run though, the sheer mass of the boat gives you a stability to die for. Here I'm thinking of one 16 mile downwind run we did in two doubles, where we basically sprinted and surfed the entire way. We whooped and hollered and were absolutely spent at journey's end.
In a nutshell, can't comment on the Viva as we don't have this marque here in the US, but for family use, the XT is a good pick. If you're on the lighter side, the Stellar is a fine choice, and the Elite is not unmanageable; just know that you will twitch a bit more, and conditions will ramp this feel up quite a bit more.
"Nice? It's the only thing," said the Water Rat, solemnly, as he leaned forward for his stroke. "Believe me, my young friend, there is nothing -- absolutely nothing -- half so much worth doing as simply messing about in boats."
'The Wind in the Willows'~Kenneth Grahame