Hi there, I would adjust the pattern at the side seam line only.  It’ll be easier and faster and then you only have to make one alteration.  Just remember that if you bring in the side seam line for one pattern, you’ll have to do the other two patterns exactly the same.   Also, whatever measurement you bring in will be adjusting the pattern by four.  For example, bring in the side seam line by 1″ on your patterns, that means you’ll actually be taking in the whole boxers by 4″.  So just don’t go crazy or you might end up with boxers too small.  If you want the boxers shorter, just bring up the hem line on the pattern as well.  Good luck!! 🙂

If you take in 1″ on the side seam of the front pattern and 1″ from the back pattern, that’s 2″ total.  For a pair of shorts though, we have 2 sides so then I just double that number and it equals a total of 4″ alteration.  Hope that clears it up.

Does he just want them to be longer? The waist size is dependent on his actual waist measurement as you’re cutting the elastic to fit his waist. The pattern waist is naturally bigger which creates the gathering when the elastic is fitted in the casing. So the size here is a little flexible. Obviously, if you cut the elastic to be bigger than his waistline, there’s not going to be anything to keep the shorts up. If he wants a longer crotch length, you can just extend the pattern at the top but you have to do both the front and the back. I would take the measurement and split it between the two. So if the crotch needs to be extended by 1″, you add a 1/2″ on top of the front and 1/2″ on top of the bottom. If he wants longer legs, then just extend on the bottom of the pattern, again doing both front and bottom, but this time you do not need to split the measurement. If I were you, I’d make a sample pair from an old sheet or cheap muslin to test the fit and then make adjustments to the pattern.