Advice on waist alteration

I've never done it in jeans, only thinner materials, so can't really speak on it specifically.

Have you tried fastening at your planned intake seams with pins or loose (hand)stitches first? This way you can try them on before the final decision and see how it would affect the pockets or if it creates odd bunching or stretching in the front or twisting of the legs or something else unexpected.

I suppose it kinda falls under "measure twice, cut once".

I'm back from class. To translate everything my teacher told me will be challenging because I barely know any of the terminology in English. I will edit this comment after looking up some stuff in a dictionary.

Update:
One option she told me was to unstitch the back of the waistband and make three darts. One at the centre seam and one in the middle of each back pocket. Then cut the waistband just at the middle so the seam gets concealed behind the belt loop. One problem of doing it like this is that 14cm is quite a lot so the side seams and the pockets will get pulled to the back 7cm each.

If the waist is 14cm too big, the hip will probably too big too. It is necessary to know how much you need to remove at the hip.

The other option has more work but would give a better finish.

Unstitch the back of the waistband past the side seams, unstitch the side seams as much as necessary to also get to fix the hip size.
At the side seam you can remove 2cm from the front and 3cm from the back. For a total of 10cm and the option of reducing some hip. Then 3 small darts at the back.
The pockets will get a bit smaller but not by much.

I had a pair of jeans that I'd altered once. (Apologies if this explanation sounds simplistic, this is just how I describe things when I can't physically point them out to people.)

There are two belt loops, just behind the hip, on your left and right side. You can conceal a small dart beside each one, disguising the fold under the belt loop. Alternatively, you can invert the trousers, don them while inverted, and pin down the outer hip-to-ankle seam and then stitch that into your preferred shape. This is easier to conceal and easier to tailor into a more flattering shape.

When it comes to altering the length, shortening them is easy. But if you want to keep the fold well-hidden, you can use hem tape to make a backing, to protect the stitches from forming an obvious crease. Granted, no one's gonna be looking much at your ankles unless you have nice shoes or they have a thing for feet. But still, hem tape will help make the thread tension less obvious.

I'm on my way to class, I'll ask my teacher in a few minutes.

Tricky, 14 cm is a lot. I second you might run into issues with the pockets. Hand sewing and trying out first is a great idea.

Guess I would try only one 3 cm dart on the back, while taking the rest from the sides. Depending on your body shape, your plan might work out as well.