Hi Janked,
Your quiver is better than most I see. The Rebel is a true twin tip kite and works best in it's mid to upper end wind range. The Neo is a great wave and freeride kite whose wind range is better suited to lower to upper middle end. Their (Neo's) top end isn't great as the kite gets shaky and flutters about misbehaving with only 3 struts, unless you have the body mass to load it. The Rebel on the other hand loves the strong wind and will handle well at the extremity of it's top end wind range. This is the big air beast, made for big wind, they tend to be a little heavy and lack the wingtip surface area for light winds, hence why they aren't ideal at their low end.
The rest of the quiver aside from getting a bit "long in the tooth", isn't bad at all. The 6m Dice would be radical fast in a good blow for you, but may be fine with your missus in moderate winds. Recommend flying this one on the smaller bar to take the "sting" out of it's tail.

At 75kg and 60kg, you are almost perfectly weighted to share the quiver you have. 10kg body weight / square meter of sail area is the general rule, so the 2 meter jump is pretty close.
Neo's are a great allrounder for twin tip and also for surfboard. On a surfboard at your weight, the 8m Neo would be your daily ride and a 6m would be a kite for the windy days. The 2016 Dice works pretty well on the waves also, not quite as good as the 2015, but still a worthy wave kite.
The power of the Neo's hasn't changed much year to year so I would suggest changing over one kite at a time, starting with your oldest (most weathered) kite. You will get a better discount buying 2 kites at a time or more, but really depends on your funds and the condition of the kites. With gear of that age, keep an eye on your bar and lines for wear and tear. Keeping up the maintenance on older gear will keep it well and truly serviceable.
I'm happy to cast an eye over your gear and advise you of condition, and what you should change, and what you can "get away with" for a while longer if you are in the area.
DM

N.B The only thing to add to this is that when sizing a quiver, working the kite sizes on equal jumps in size doesn't work (especially if it's a quiver just for you). The difference in size from a 4m to a 6m is 50% larger, from a 6m to an 8m it's 33% bigger, 8 to 10 is 25% bigger and 10 to 12m is obviously 20%.
What this means when sizing out a quiver (when not sharing with the missus), is that you need to scale sizings by percentage. Ideal sizing would look something like my foiling quiver of 18m, 13m & 10m, or my old quiver of 21m, 15m, 11m, & 9m. This prevents too much overlap in wind range. This is for others who are curious, not necessarily Janked as the shared quiver works differently