Focus on the spin and not the press while you're learning them. Its hard to say exactly what to do because there are a lot of different styles of buttering. But focusing on the spin to learn them and then learning how to press them more from there has helped me in the past
Get a little more air time and don't open up. It's the same thing when trying to go from 360 to 540 off a jump. All you have to do is set the rotation and don't open up. When you come around at 270 catch the landing in your eyes for a second but don't let your shoulders stop. Stay composed and look back at the knuckle and be ready to get your feet fully around. You can probably get away with doing butter 450s and shuffling it around the first few times and as you get more comfortable just fully commit.