Leaving aside the physical issues with elephant-sized insects (and they are many), humans would survive them the same way we survive every other animal species: avoiding their territory when possible, making targeted strikes when we know that a dangerous animal is in the vicinity, and taking advantage of weapons.
The first key thing to realize is that populations of large animals can't be too dense. If they are, there isn't enough food in the area to support them and they must migrate or starve. In the case of carnivores, the food is measured in herbivores; for herbivores, it's plants, but the principle is the same. (For plants, lest you think you can get around this with megaflora to go with your megafauna, the limiting factors are a mix of soil nutrients and available space to catch sunlight.)
Complicating manners, cobras and scorpions are not known for living in large, contiguous family units the way elephants are. Mostly they're encountered one at a time, and the larger versions would likely be the same way. Some wasp species are eusocial and live in large family groups, but mostly likely these would not be able to feed themselves at giant size, so you'd have to start from the solitary wasps.
So instead of huge packs of roaming monsters terrorizing your humans, you're much more likely to be dealing with individual predators with territories from which they drive all other large predators (they have to, or there won't be enough to eat). For the most part humans can simply avoid predators' territories by sticking to their own colony boundaries. Most fatal encounters with animals happen to unfamiliar humans who blunder into the animal's territory; the reverse, with animals actively preying upon humans, can happen but is rare enough that it won't cause an existential threat to your colony.
Simple enough, but what about when you need to expand? Well, the answer is really extremely simple: guns. No matter whether your creatures' chitin is scaled up or not, it won't protect them from larger-caliber bullets. A few pickup trucks with machine guns in the beds would be sufficient to cut off a rampaging giant, herd it away from other humans, and if necessary kill it, all without allowing it to close and attack. (Wasps would need slightly different tactics - they can fly, and might be a good deal faster than the others depending on how you went about solving the scaling problems. But their wings are huge, vulnerable targets at that scale.)
If your colonists don't have guns for whatever reason, their options are considerably more limited but by no means spent. A combination of pit traps for larger animals, nets to slow and ground wasps, long spears, and fire should be sufficient to dispatch pretty much any animal - especially a large, solitary one.