Feathers McGraw
There's a fairly large level of misunderstanding around this stuff - I know, I have a background in geology.
Katla always has a fair amount of tremor - but the devil is in the detail. Pretty much all the tremor in Katla is very shallow - less than 1km deep. It has a very active hydrothermal system - geysers and hot springs etc under the ice cap - and that's where the tremor is coming from, harmless hydrothermal activity. There's no particular indication it's close to an eruption.
Laki wasn't a volcano in itself; the Laki eruption was a very large fissure eruption from the Grimsvotn volcano. It does those sometimes, as do Katla and Bardarbunga, but many hundreds of years apart. Grimsvotn is pretty close to an eruption right now, it could come in weeks or months - but, since the last Grimsvotn eruption in 2011 was very large, the next one is likely to be small.
Then there's Hekla, the wild card - it's pretty unique, it generally erupts with virtually no warning signs, and can do at any time. Its eruptions are initially very violent, but tend to calm down quickly after a few hours into relatively harmless lava flows.
(Eyjafjallajokull, the one that caused chaos in 2010, is now safely back to sleep and likely won't wake up for another couple of hundred years)