The Simple Cub has been touted by a few as a good plane to learn to fly with. Most would disagree. But if that's the plane you've got, then let's work with it.
Ground launching is difficult for a new pilot, but will give you more confidence, once you learn to fly. Since you've got someone to hand-launch your cub, try this:
They need to hold it underneath, just so they're comfortable with the balance. Add just a tiny amount of up elevator. You've got to bring up the throttle to about 75%. Your brother has to EVENLY THROW the bird into a light wind at just a little above the horizon level. It's not like throwing a ball. It's more like pushing the plane with force with follow-through into the desired vector.
You've got throttle. You've got a bit of up elevator. You can expect the plane to roll rapidly with the torque of the engine and propellor. You've got to immediately counter. The little bit of up elevator means you won't be pointed at the ground, but if you're not careful you can point straight up.
You've got to be quick on the sticks and smooth things out. Then you just fly until you crash. Then you rebuild and do it again. Pretty soon, there's a whole lot less crashing and a whole lot more flying!
You are firmly on the road to RC flight success! I wish you luck and keep us posted, so we can help and cheer you on!