Are Compatible Minifigures Legal to Make?
Yes. The core brick patents expired long ago, so making and selling major brick compatible minifigures is legal; only the brand names themselves are trademarked.
Yes. The fundamental patents on the classic stud-and-tube brick design expired decades ago, placing the basic interlocking design in the public domain. That's why many companies legally make and sell compatible bricks and minifigures.
What remains protected is the brand names and logos of the major manufacturers, which are trademarked, so compatible makers can build to the standard but can't use a protected name or pass their products off as genuine. Quality makers brand their own products clearly. (This is general information, not legal advice.) Browse quality compatible figures in the Brick Bros minifigure collection.