In english we differentiate between "Talk with" and "Talk to". While they mean the same thing normally, they mean different things if you put emphasis on the particle. "Talk with" means have a conversation together while all/both members take equal part, whereas "Talk to" means you're talking at the person/people, that you're speaking and they're just listening, and it typically implies that the person doing the talking towards the other person/people believes they have some sort of superiority, at least in the context of the conversation.
Is there an equivalent to this distinction in Swedish?
agree with person222222 entirely.
also, a closer translation of "dyker upp" is "show up". In the USA, it is rare to expect people to simply "appear". This is reserved for ghosts and other supernatural arrivals that come out of nowhere (or seemingly so, like a theatrical entrance). In everyday speech, it is VERY common to use the phrase "show up" or "get here" or "arrive" or "come" when referring to the event of someone finally attaining their destination to where we are and making their presence known to us so we can have that conversation WITH them.
"We are talking with them" means it's happening at the current time. Combining that with "when they appear" doesn't really make sense because it's specifying a time that is not at the current time.
("We are talking with them" could also be used in a general sense to mean "We're in negotiations with them," where the physical act of talking isn't occurring at the current time, but it's still conveying that the negotiations are in progress at the current time.)
"We talk to them when they appear" means they are repeatedly appearing and disappearing, and during the time they are present, we talk to them. (It's a peculiar sentence, but it's at least possible.)
"We will talk to them when they appear" is the most likely translation, meaning we expect them to appear in the future, and at that time we will talk with them.