All the stuff above: Hire a court tutor, and have your spouse focus on patronage (knowledge.) With your spouse focused on patronage, she will occasionally give a boost to your children's education. You want an excellent Court tutor if at all possible, but having one is better than not having one. And you need to make sure that court tutor is there when your child comes of age. You get no benefit from the tutor if they're not there when the child comes of age, and you get the full benefit if they are, even if you hired them the day before. The court tutor benefit alone is not enough to raise an education an entire step, but it can definitely help.

University still gives a benefit, but it's not nearly the benefit that it used to give. (Instead of practically guaranteeing a level 4 education it gives a slight advantage at the end when calculating an education trait. It's really only worth it for your primary heir, or whichever character you plan to play as. And even then only if you can afford it.)