So I suggest you start with just one hive.
and
Now for winter as close together as possible,
There will/ should be plenty of time to consider these, as you appear to have no colonies at present. It is always better to start with two colonies if practicable.
As Finman suggests, but needs must, so as long as you have top side of 2m, or very close if under, you can leave just enough space between them to set down the hive bits when inspecting, and leave enough access space for yourself if working from behind (the normal if frames are warm way). Working from the side (frames cold way) may mean better 'exit opportunity' if the parts are deposited in front or behind the hives, but a metre space should be adequate for most situations
Hive type might restrict your choice of frame direction, of course.
To actually answer your question, you can leave very little sparation and a divider of some sort between the two hives might be appropriate if you felt it necessary. Indeed, you do not need the full width of the entrance, ever, if 22mm deep, so the entrances can be effectively separated by that means. Simple, only half the entrance used would afford about a half metre separation.
Of course, we do not really know if your garden is suitable at all and even it it were, you would be well advised to search out alternative accommodation for any time the occasion may arise, So, as EB suggested, get a local experiencedbeek to assess your proposed siting. There is little worse than bees sited inappropriately at the outset.
