I don't think the impatiens have anything to do with it. I'm not sure what the problem is with your geraniums but mine always get botrytis, a fungus that makes the leaves yellow and fall off. I stopped growing them for that reason.

Sorry, I forgot to add that geraniums like sun and impatiens like shade, so that may also be contributing to the problem.

Geraniums definately need sun, they also need less water than impatiens. I had a bed (sunny) with geraniums and impatiens and I had to water the impatiens quite often, while the geraniums required watering much less frequently. They weren't planted that close together so I could be selective with the watering and all the plants survived. It could be overwatering that is killing the geraniums.

Absolutly, the geraniums will do best if the soil is quite dry between waterings, the impatients need steady moisture and to never reach a dry state. Best companion in annuals for geranium can be the petunia, and perhaps for the impatien it would be......more impatiens!