I used a brush and painted all of the walls just under the crown molding then took a roller and painted the room. The painting I did with the brush is now darker than the walls even after rolling on two coats. What did I do wrong?

Garage last painted 15 years ago. As I apply new paint the old paint peels off of the wall and sticks to the roller. The walls are drywall.

Please can you help. I had my door stripped back to the wood I primed them before painting and yellow streaks keep coming through. I then used Polycel stain block painted this on and two weeks later the yellow streaks have appeared again, what can I do to cover these

What kind and size of the brush do you guys use when cutting in stucco?