Hi Michael and Susan,
I'm not sure you are going to get the really "light wind planing" you seem to desire on the Gemini with sails as small as 5.4 m2.
In 12 knots, I sailed the Gemini with both light weight women and some farily heavy weight (100 Kg +) guys.
We used a 9.0 Gator as the rear rig, and a 6.0 m2 Power Drive on the
We were fully planing in 10-12 knots.
So, perhaps with a larger rig on the back (than your 5.4 m2) you and Susan can have an absolute blast on the Gemini.
If you purchased a 7.5-8.5 m2 camless rig (Gator, Retro, etc.) as your
"light wind motor" for the back of the Gemini, I think you would be flying along in a solid 12 knots. Give Susan your 5.4 m2 for the front sail.
I took a girl (the Trade Show coordinator from Atlanta) that had never been on a board before out on the Gemini with the 6.0 m2 Power Drive and 9.0 m2 Gator combo, and managed to get us planing even though she really didn't understand completely what to do with the sail.
She was thrilled, I was stoked.
As far as tacking or jibing, you can do either one with a little practice (and a lot of coordination between the 2 sailors).
You will never hear more "laughter" than when 2 inexpereinced "tandem sailors" first take the Gemini out on the water.
They will be having max fun and will also be alot of fun to watch.
The timing of the "sail flip" on jibes is quite interesting.
The front sail goes into a complete wind shadow just before downwind and this makes getting the front sail flipped a whole lot more interesting. But the key here is to sail the larger "back sail " clew first out of the jibe, and have the front sailor "duck" at the right time to get the boom to go over their head.
You can do "duck jibes" really well, but if the rear sailor "blows it" the front sailor is not going to be happy.
As I said. lots of laughter, shouted gleeful "instructions" on the timing of sail flips and such. Most fun two people can have on one board!
Hope this helps,