Throwing together pre-made juice and DIY juice are two different things.
Throwing or guessing with nicotine is not condusive to long life as you mix with much higher nic strengths than you vape.
If wife is doing the mixing, I'm not sure how the husband getting a crash course on mixing is going to help. But then again I've never figured out how to teach a female anything except firearm safety without it ending in a big fight.
The previous links to calculators will be a huge help. Going to the DIY e-liquid sub-forum and reading the stickys will also be very helpful.
Mixing is like cooking. Some love to do it, some have to do it, and some would have someone else to do it.
Get an understanding of how the calculators work and then go from there.
As long as the kit you pick has nic, plain PG, PPE, measuring hardware, and empty mixing bottles, you can always add to it. Getting some flavorings and VG with it is always good.
And get ready to gracefully play taste tester...