With our second kid now 5 months, first thing I'll say is that what you can get away with regarding travel can be vastly different from kid to kid. Our first hated being confined and has always been brutal to travel with. After having that as a frame of reference, it blew our mind on our first longer car trip with the second baby that she just sits there quietly the whole time.
At 6 weeks it will depend on a lot that you can't predict. That's earlier than when a lot of people would feel comfortable leaving their kid, unless grandparents are pretty competent with babies. At 6 weeks, you're still in that constant feed/nap cycle and lots of night wakings. Honestly if it was us, we would wait to celebrate until the baby was old enough to spend a few nights at the grandparents house (could be 6 weeks, could be 3-4 months), and go on our own. The first 2-3 months can be exhausting enough as it is, trying to force a vacation in there with a newborn might end in a lot of frustration. If anything isn't going well, like naps or feeding, being on vacation will just make it that much more stressful.
Bottom line, for myself and almost anyone I know with kids, until they're old enough to enjoy the trip themselves, leave them with the grandparents if the option is available.
