What is the persons posture? A stooped person has a rounded back vertical and width wise. Round means longer. The total circumference doesn't change. This means that the front is shorter length and width. The opposite for erect posture.

The front neck points are long and the back neck points are short from the hem. To balance this out "slide" the backs up on the side seams. The the back shoulder seam is trimmed where it overlaps the front. Perhaps the top front could be trimmed, if the armhole gets too deep. The top of the back sideseam is trimmed or folded. Part of the hem is used to fill out the bottom length. Some people need the fronts moved out on the shoulder seams to help line up the fronts. Which requires the front of scye to be "scooped out". The reason for this is the chest needs to be narrower, which sometimes means the back needs to be wider. Having inlays in these places is a requirement for this method of correction.

Is it possible to get the shears welded back together? Pipe fitters at oil refineries are extremely good at welding. Read that the handle and the blades could be different materials welded together. If so, you might need to do some research. If the welder doesn't know the lingo that would probably be the wrong welder. Decades ago I watched a video of a French blacksmith hammering out a pair of shears. In those days they made them for the individual like tailors make clothes for individual.

Another thought. Which side are you pressing from? The underside shrinks the most.

One old tailor said when you fold the pleat over into place put a little bit of slack on the top layer. What may be happening, the top layer looks short and is pulling back, therefore, pulling it open.

It seems the Brits cut a narrow sleeve. Tailors from other places the cultural norms were different. Wider sleeves and no shirt cuffs showing. Shirt cuff showing is rather flashy. More suitable for the city. The world has changed. We don't travel in buggies and wagons. Tires last more than 3,000 miles. Flats are rather rare, instead of normal. Some clothes are more decorative. Changing a tire in 30 degree minus weather with shorter, tighter sleeves is not practical. And, coldweather can be dangerous. Clothes still need to meet local basic demands. There are fewer of these demands. Some about clothes are about fun. Shirt cuff extended makes less wear on the expensive coat cuff.

Put a damp rag on it and put the hot iron it. Some cloths the bottom layer will shrink. Otherwise, take the seam apart and hand sew it so it slightly rolls in. Don't want the roll noticeable to the untrained eye. It's a smart looking coat.

The first I learned about hand made buttons is to use two strands of buttonhole twist. Lay them side by side. On trousers they are more flexible. A business suit gimp might have the best appearance, sometimes. A sports coat is very different coat. I would think for most a softer buttonhole. Whatever the customer wants. It's theirs.

Here is one from Maurice Sedwell by Andrew Ramroop. https://youtu.be/sjHZiyrACkY?si=mSPnhTiNjXFK2xCM

Practice makes perfect. Sometimes it never seems true, at least, not soon enough. The knots (pearls, purls) pulled to latch- is tight enough. The knots setting a little higher look best. Pulling the thread, not the needle, up and whatever direction, getting them in a nice straight line and setting the proper height. With practice you will be making fewer and fewer movements as your skills develop. Clothes that go in the regular wash, jeans for example, I won't use silk twist, but sewing thread, two strands, not twisted, but side by side. I like the look.

Some men have narrow shoulders. Some tailors make the shoulders of the coat broader to give the appearance that the man has broader shoulders.

A method is written here. Sometailors use this method or similar. How to Make Men's Clothes. Some tailors always run two layers of pocketing up to the waist band. Some don't. Cheaper pants in warmer weather, Ones enough. Two layers is stronger.

Knowledge can come from anyone. His books are good. Some parts are hard to understand. His instructor at Tailor and Cutter was Phillip Dellafera. His diploma was huge hanging on a wall in his house. His coat making book has useful information about fitting coats. It might help you in some areas. Good tailors explain fitting problems the way they understand it. If some of his methods help you understand how to solve some problems, then you have won. Sometimes you might want to use his method and other times some other methods. Having a number of books on this subject is well worth the money, including Rory's. Grandfather said one pin at mid shoulder to find balance. This is quick and easy. Pull the pin, shift the front up down, left right, diagonal to best location. Move the back up down. Pin mid shoulder again, then neck shoulder point (fronts parallel). How much padding at end of shoulder. Decide shoulder seam location. He put it out sight of front. Decide what kind of sleeve cap. Etc. Different ways to achieve desired. Different books point out different things. The more the better, sometimes. Rory has his own thoughts worth reading and learning.

If you use sawdust make sure it is cedar or similar. Cedar keeps bugs away and stands up to moisture.