I taught myself at age 19. I thought it was about time I learned, and it was worth it.
I had the new bike, purchased the day before (and slowly wheeled home on foot)
I took it to a private estate of quiet roads and had a go at rolling it downhill for a little momentum and getting my feet on the pedals. Once you are moving, the balance happens and it's as easy as... riding a bike. I find that with my DCs too. Their hurdle is getting that first push to move. I learned to pedal and balance in that one session.
I did have a mishap when the gradient increased and being still in the first gear, was going way too fast and ended up being brought to a halt by the kerb of the far side of the bend in the road. Thank goodness no cars were around!
Once you have the feel of the balance, that's it, you have it. I find it similar with the DCs too, although if it's been a while they can forget. I have had long phases without riding and can always get back and do it.
Generally you need the back brake more to moderate speed and the sharper front brake less frequently.
I'm not fantastic with gears. Generally a mid-gear will get you through most cycling. Maybe lower for going uphill to reduce effort, and higher for downhill going fast, but that's not an immediate concern. You need to pedal when changing gear, and it can feel jolty, so save it for when you are happy with balance.
The skill I struggle with is balancing with hand signals for road cycling, but I mainly cycle off road or very quiet estate roads. I avoid major roads.