These are wasps and not bees; specifically, they appear to be Yellowjackets. Several species of Yellowjacket occur in Maryland and we can't see enough detail (understandably, since you can't take a closer photo and they're not holding still) to determine which they are. That said, which species they are doesn't really matter when it comes to removal options.

Yellowjackets, like other social wasps, do not re-use nests from year to year. (Very, very rarely they might, if a nest was kept warm enough in a wall void over the winter.) They cannot be relocated like a honey bee colony could, so yes, dealing with them via a pest control professional would involve killing them as the nest is removed.

You can't block the nest entrance to keep them away since they will only chew a new one in order to escape, since they need to come and go to forage to feed their colony members, and that secondary entrance might happen to be inside the house instead of another outdoor gap/crack as the entry point. Therefore, the only recourse is really to just try to avoid them until they die out by winter (granted, you said that's not really feasible if they have been stinging) or to have them treated with pesticide. You could use wasp spray yourself or hire a professional to treat/remove them for you. If you spray, follow all directions on the can carefully. It would be best to get the old nest out at some point, even if this waits until water after the nest is treated now, since dead/dying wasp adults and larvae could serve as bait for rodents or other animals looking for an easy meal, which of course we don't want inside a wall. Afterwards, any gaps or cracks the queen originally used as an access point to get behind the siding this past spring can be sealed to avoid the problem arising again in a future year.

This time of year, social wasps generate some new queens and males in the colony, and these eventually mate and disperse, leaving to overwinter by themselves and to start their own new nests elsewhere the following year. (The queens do, the males just die soon after and don't survive winter.) Although workers and queens/males might have very similar body patterns, there can be enough differences in pattern and size of the individual wasp that they may look like a different species among the other workers. This might be what you are seeing on that piece of foam insulation or weather-stripping material outside the nest entrance. Even if it's another Yellowjacket species entirely, that doesn't necessarily mean there are two nests (it's unlikely they would tolerate being that close to each other); it could just be one worker from another nest further away trying to steal food or is curious about the foam for some unknown reason. (Wasps create nests out of "paper" they make themselves from wood pulp they chew off of bark or fence posts, so this would not be something they'd be gathering for nesting.)

Miri