How do I stop Safari on my iPad from reloading tabs once they are already open?
Probably not.  You need to think of the nature of the iPad.

It is RAM constrained (and battery constrained, but that probably doesn't affect this as much as RAM), so it often suspends apps so they can be "reconstituted".

Depending on what you do in the week (a long time in app land) the pages would be suspended and removed from memory.  Reopen the browser (and this would be any browser on the iPad, not just Safari) it has to get the pages again to show.

So.. this is what iPads (and to some extent android devices) do.  It remembers where you were and re-gets the page.  Now you could do a Reading List, or even use Pocket (I think Pocket takes a snapshot in time, so may work better).  Those may bring you closer to where you want to be.  But the tabs will be reloaded, because they were gone way before you re-opened safari