Oh my goodness! You very well could have a goose. That egg is huge! I’m not totally sure though since I’m not an expert on African geese. But congratulations if you have a goose! That egg is something to be celebrating!
I would say they’re both ganders. Females don’t usually stand like that, at least my girl doesn’t. I’d say you have two ganders. But if you show a video of them talking I think that would give a definite answer.