the orcs would probably find a hole into one of these lava canals and build a heating system on top of it, and then build their longhouse over and around that heating system (a simple chimney with metal sides, to absorb as much heat as possible). I think that in this kind of environment wood would not be a common resource, but volcanic rock and tuff would be very common, there are several ways how you could handle this wood situation(wood is very important resource) and build this area/biome.
there is a short warm period(much like spring in Siberia), that allows plants to grow, volcanic ash works as a great fertilizer, because of its high mineral content. So the orcs would have a short farming season. and there would be some trees around.
the land is a frozen wasteland and instead of plant matter, orcs use bones, shells and other bodyparts of huge long-dead animals. Some orcs scavenge icebergs for ivory to sell and occasionally they find entire frozen mammoths or other animals, with their meat still intact(this actually happens irl).
both of these could exist simultaeously option num. 1 would count for people living under the mountains, while num. 2 would count for orcs living in highter altitudes.
if there are any areas that are warm for the entire year, like a delta of lava tunnels, that heat the ground above, then that is a great area for lizards and snakes. maybe orcs use these snakes to catch rodents instead of cats, but only the non-poisonous ones, to keep their babies relatively safe. the snakes would also gather around heat sources to rest, just like cats do.
Now you could give your orcs access to metals, that the volcanoes provide. they could work in mines that are extremely dangerous, because of poisonous or explosive gasses, or with a risk that they will mine into one of the lava tunnels and flood the mine. Or the volcanoes could errupt in random intervals, throwing big shards and chunks of useful minerals and even gems around them. Which would be a big event for scavengers.
They also need a forge to melt the metal, unfortunatelly most lava sources don't release enough carbon, to make proper steel, so the orc capital would be probably centered around a source of good carbon rich lava and the rest would have to use charcoal to make steel, carbonizing already scarce wood.
they would also have access to minerals like sulfur,phosphorus or fluorine, this is where your goblins come in play. they could process these minerals, creating acid, blackpowder, luminescent lamps (decreasing chances for the gasses in mines to explode). Don't forget to include shamans that would use volcanic gasses to enter trans states, just like in Delphi.
If you decide to give your orcs an access to sea, they will hunt fish, seals, penguins. and collect clay for ceramics and sand for glass. in case they find big chunks of semi-gems or volcanic glass they could make containers, furniture and ceremonial jewelry from them.
You should avoid the usual VIKINGS!!! cliché. No community can sustain itself just from raiding, even Mongols and Huns settled down or were really good with moving their lifestock, and if they could burn down villages and beseige cities, why would they not settle there? (vikings colonized all kinds of places and were good traders.)
So here is my verdict: If you are looking for typical barbarians, then this is a bad setting for them, you should use a tundra like biome for those. If you will place a civilization in a place with free energy it will prosper and develop. these orcs would be unusually developed from standard fantasy orcs, both culturally (ivory, rare metals, probably even dragon/dinosaur remains and temples) and technologically (rare minerals, metallurgy, dangerous mining, chemistry)
I hope this has been helpful :)
