<<EDIT - Retracted - read subsequent posts for more correct answers>>

Note that the kit shown has 2 sizes of pins, use the larger of the two and go to town, have done it many, many times before, I suppose if you're really nervous you could solder the crimps afterwards but I see no reason to.

Caveat - I'm a software guy, open to opinions from hardware folks....

Oddly enough, the photo in that article: "How to convert IDC looped terminal pins to crimped pins" by Ed of GPE uses two wires in one crimp.

Had to re-read this, he also states that this type of crimp is "illegal", so it looks like the the third wire option is the best solution.

"There are two tricks to making this work. The first trick is to solder the wires to the terminal pins as described above. That is, lightly tin the two wires with solder before crimping them. The key is to tin the wires very very lightly. If too much solder is applied, the wire diameters will be too large and both wires won't fit in the single terminal pin. Also do NOT twist the two wire together, keep them separate and tin them separate. Then after the wires are crimped, gently heat the wires and pin (without adding any new solder) to melt the existing solder, securing them all together to the crimped pin.

The second trick is to use the insulation-grabbing part of the terminal pin as an added area for the stranded wires. Because the insulation-grabbing portion of a crimped terminal pin is larger, this additional area handles the two wire together fairly well, without spilling-over the stranded wires outside of the crimp. Though this is definately not how to do a proper crimp, in this situation there really is no alternative. Note a bit of practice is needed to get a feel for this "illegal" crimp.

An additional thing to remember is there's limited space inside the plastic Molex connector housing for the two wires. So a clean and tight crimp must be done. Be sure to inspect the crimp carefully for any stray stranded wires that could short to adjacent pins after the terminal pin is inserted into the plastic connector housing."

IMO - have to disagree on this point, I can strip two wires and crimp in very little time, it's neither difficult nor time consuming, it's just not the best way.

I would also argue logically, given the crappy nature of IDC connections, that the two wire in one connector method is probably superior to the IDC it is replacing.

But in the interest of the OP, the third wire method is the way to go per Ed of GPE, and he is an expert, I am just a hobbyist.