I think you should differentiate between your tent and the kids's tent. For the kids a 130 cm wide two person tent is fine, as long as there is some space for some luggage (something like a Hilleberg Nammatj 2). For you, however, I would not go below a 160 cm wide three person tent with a large porch such as, again by way of example, a Hilleberg Nammatj 3 GT. You will have nearly all the lugagge, and if the weather happens to be bad, you want to be able to huddle together for an hour or so in your tent. We used to have the Keron 4 GT and now have the Nammtj 3 GT and would not want to have anything smaller for als long as the kids will come with us. In fact, my wife thinks it is too small. She would have preferred a Keron 3 GT for the extra luggage space.
As for length, be careful with tents that slope at the back. Our 220 cm Nammatj is only just long enough for my 177 cm length. With my feet in my sleeping bag I do touch the inner tent cloth from time to time.
Willem