The ants, flies, and wasps are drawn to a sugar source called extrafloral nectaries. These are normal structures on a variety of plants, peas included, that produce a nectar-like reward for insects outside of the flower. They attract insects like ants and wasps that help the plant defend itself from plant-eating predators (mainly other insects), since both ants and wasps hunt other insects for food. Any wasps drawn to the sugar are not likely to bother people as long as they aren't swatted or grabbed directly.

The poor seed production in the pods could be due to heat/drought stress (high heat can kill pollen, even in self-pollinating plants like these), low soil fertility, plant crowding, or some other environmental factor. Stink bugs (and some of their relatives) feed on developing seeds by piercing the pods, and sometimes infect the seeds with a disease in the process. You can look for signs of bug feeding on the outside of the pods (puncture marks, since they have fine straw-like mouthparts that suck sap) and on the seeds themselves (they would be malformed, rotted, or shriveled). Deformed or badly-damaged pods can be trimmed off and disposed of so they don't harbor any pests or diseases that might spread further.

Miri

Miri,  Thank you so much for your quick and thoughtful, detailed reply. Very useful information.  Thanks so much for your help.

You're welcome.