Will your farmers jack incorporate a catch-bit? Either way, no crinking of either blade, offset grinding will do the trick. I would offset both main and secondary. With no catch-bit both need to be offset ground. With catch-bit its possible to not offset grind the secondary but it really gets tight without rubbing and then it is even harder to get as much secondary blade in as possible.
In the two farmers jacks that I made as examples show below, they are considerable different in grinds. Both single spring, the stag does not use a catch-bit. Both blades are offset ground which manifests itself with a very deep plunge line on one side.
The ivory example uses a catch-bit and while both blades are "offset" ground it is done much differently. The sides of the blades that face each other have no plunge line at all. The tips of the both blades when ground favor the liner side. Seems confusing a bit but hope it makes sense. I think the grinds that was required on the ivory example was probably the most challenging grinds I had done on any of the multi-blades I built.
Good luck with your build!