For the hornets, sevin can be bought in a liquid form in a container that hooks to the end of the water hose. Hit them in late evening but early enough that you can see well enough. I had good luck with it on a nest of ground bees that attacked every time I went within 10' of it with the riding lawn mower. (You know, those big ones that "don't sting". Found out they do and its quite painful). Beats me how they know to nail you right in the middle of your back!!. Was able to stand off about 15' and soak the opening with a coarse spray, so they thought it was rain. They were gone in 2 days. Also works on yellow jacket nests.
That said, I only nuke the critters that are a threat because of their location. Lots of the "dangerous" bugs control the population of the "pest" bugs.
Go
Of course the decision is up to you, what you use... and the risks are yours to decide if you want to take. I watched my brother in law use a can of starting fluid - it worked really well, it froze the hornets to death... along with their nest eggs. The starting fluid evaporated quickly too. I suspect anything that's not highly flammable like starting fluid is but still creates a instant freeze would work just as well. My bother in law, like me - is not into chemical pesticides that tend to linger for long times in the environment.
Another thing that I know that works is Seven dust. It may not work instantly but will over time. My neighbor dusted his veggie garden with Seven one day, and for weeks afterwards I found dead honey bees, yellow jackets, hornets, wasps and various other kind of flying insects dead in the flowers of all three of my veggie gardens. I don't understand the logic behind his dusting his garden with seven, bees pollinate the flowers - so the plants produce vegetables, but hey I'm not that smart either... Every since the "mass killing" a month and half ago I've had to spray my vegetables regularly with blossom set in order for them to start producing again. The neighbors garden has long since died since he failed to keep it watered during the long hot spell. I lost a good 3 weeks of veggie production due to the mass killing and the bees have not returned yet

Time to move to the county
I know... not WWing related and highly opinionated, delete if needed - thx