Hi there and
to the forums!
Are you sure on your budgies' gender? I'm asking because often, groups of budgies with uneven gender distribution (i.e 3 of one gender and one of another).
Feel free to post pictures of their ceres taken in natural light and we will be able to confirm their gender for you!
Also, is there simply not space for Pinchy? Perhaps he doesn't fit on the perch with them. In a cage with many budgies, you should have multiple food/water bowls and many of the same perches or swings at similar levels of the cage so everybudgie can find a place to perch.
Unless there is actual bickering/fighting going on, I believe the best course of action is to monitor their behaviour and see if Pinchy is excluded a lot and this behaviour isn't just due to a lack of space in the cage. If he is being left out, then perhaps separating the budgies by pairs (2 to a cage) can help them bond better and help everyone feel included.
Keep us posted on how things go!
In the meantime, be sure to read through the forum articles and "stickies" to ensure that you're up to date on the very best of budgie care practices! If you have any questions afterwards, please feel free to ask as we'd love to help