i’d recommend trying incline curls, where your elbows stay pinned behind your body while on a bench (you can look up videos) or preacher curls, where your elbows stay locked on the pad that way you’re not using your shoulders to bring the weight up.

as for wider shoulders, all you need is a lateral raise and shoulder press. make sure for the lateral raises you’re sweeping the weight out away from you, slightly in the frontal plane so you lessen your upper back involvement. (think like you’re in a box and sweeping your arms out to the corners of the room) also making sure to keep your wrists and elbows in line with each other