If light to medium multi engine aircraft are coming into consideration, my cautions expand.
then a MEP twin is your only reasonable option. There's this huge illogical resistance to twins these days, but they are great choices compared to the alternatives. They will be cheaper to run and own than a SET, safer and can carry more than a SEP.
By choosing an Aerostar, Adam has sidestepped some real concerns about light twins. An Aerostar will do the job, but that makes it unusual. A C 310 and Aztec are about the smallest twins which really have what it takes to claim "safer" than a SEP. It takes a lot of nerve, but in many light twins, the failure of an engine in anything other than cruise or descent is the cue to choose a landing site in view ahead, and prepare to reduce power on the remaining engine as you set up a forced approach a little further on than the SEP would have glided. These aircraft require great skill to climb away on one, with any kind of load. There are very many accident reports describing pilots who thought they could do it, and could not. The difference to a SEP? The SEP pilot who looses and (the) engine, knows they have a forced approach in their imminent future, and make the most of it - wings level!
During twin flight testing I have done, even up to Navajos, I have advised and briefed that an engine failure on departure will be cause to initiate a forced approach ahead, rather than a go around. No one has ever disagreed with me...
I recommend the following article as an eye opener:
8740-25, Always Leave Yourself an Out
I've never had all six of us together in a car in Europe, but certainly in Canada and the US. Yes, there are also horrendous car accidents, but your more common nuisance car accident does not kill everyone in the car. Too many aircraft accidents do. A difference will be the Mrs. She is your team member in the car, quelling the kids, and supporting you. In the plane likely she's as out of her element as the kids, and of little help to you in quelling them, so you solo have a plane and five people to please.
Personally, if I needed to take my wife and four kids in a plane together, I would, but perhaps a difference is that they have flown with me in sub groups for more than 20 years, so it's not so far out of the norm for them. I guarantee you that loading the whole family into a six place plane is going to create some uneasiness, unless they are experienced fliers. To test my theory, take subsets of them on one hour long trips to another place. When it's all smiles for everyone, things are looking up. You'll know for sure, when you have a WX or MX delay for a day or two, at a truly boring place, and a skuzzy motel. If they smile through that, you're in good shape.
Speaking personally, from 40 years of flying experience, there have been many times I was very happy not to have pax, as the flight got very scary, or otherwise annoying, I was scared or annoyed, and was in no mood to Mr. nice dad hubby. When the family is delay grumpy, and you're miffed about the cause, it all goes bad fast. Avoid! The relationship you know with your family will change for the more stressed when you mix a trip in a plane into it.
One thing which has worked a few times, has been a fly drive holiday (if your Mrs. is really co-operative. and likes to drive). Fly the two or four seater and she drives the route. Land everywhere along the way, and change pax, everyone gets a turn along the route.
Happily, I can state my experience and opinion without knowing the experience of other posters (so if I'm insulting any of you, sorry) But, I would not send any of my family with a pilot of less than several hundred hours experience on class and conditions, and well into the thousands of hours experience, were it to be all of them on one flight.
I'm not writing to discourage buying a plane, anything but.... but I would make a lot of effort to dissuade a several hundred hour friend from buying a six place to fly the whole family around. I would (do) advise to buy small first, and grow if it works.
I just know too much about GA flying....