Although I'm a musician, my kids all have outside teachers and regular lessons. On violin and viola I am certainly qualified to teach them during the first half dozen years or so, and in actual fact I do quite a lot of the actual teaching, probably the vast majority of it in the early years. But we've found it extremely helpful (perhaps even totally necessary) to have the structure of weekly lessons to keep us on track. The younger three kids have weekly lessons with their grandmother. It's still in the family, but we are able to make it a semi-formal occasion by having scheduled lessons at her studio just like all her other students.
It's not that my mom is more skilled at teaching (though she is!), nor is it that she's more controlling and demanding in terms of practicing. There's no 'good cop, bad cop' scenario at play. My kids and I just find it extremely helpful to have that weekly goal or benchmark. Learning to play an instrument is a big long job, a little like hiking a long trail up a mountain. Working at home without weekly lessons is like huffing and puffing up that hill in the woods where you know (because your legs are tired and your heart is pounding, and walking is such hard work) that you're climbing a hill, but you have hardly any visual cues to show you your progress. Having weekly lessons is a little like hiking that same mountain on an open trail of switchbacks where you can see the view and pause at each switchback to see where you've come from and where you're heading and enjoy the view. My kids enjoy their lessons 99% of the time, and also really enjoy the sense of community they get from being involved in a studio of students studying in more or less the same way.