Not any more isolation than expeditions to Antarctica in the late 19th and early 20th century.
Less, actually. There were no telegraph lines on the Antarctic expedition, and I don't know how effective radio was (not very in the late 19th century obviously). Aside from when the two planets are on opposite sides of the sun, communication will merely have high latency. We'll be back to sending podcasts and video messages, not chatting on Skype, but it's still quite a bit better than what those early explorers faced without even leaving the planet.
When the two planets are on opposite sides of the sun (which is what, a period of less than a week happening less than once a year?), a third point will have to be used to "go around", reducing bandwidth and adding to latency, but it's still better than nothing.