Nice trees, good material to learn how with.
First, make a plan, what would you like for each of these trees, draw out a plan if you want.
Key question, how large or small would you like each of the finished trees?. The answer determines the diameter of trunk needed, and that will determine whether you prune anything at all this year.
Normally one keeps a lot of foliage, long branches, until the trunk is close to the desired diameter, more leaf surface area, quicker the trunk increases.
1:10 to 1:3 are common ratios for diameter to height. A tree as found in a forest might be 1:10, a mature tree in an open field might be 1:5 or 1:4. An ancient tree might be 1:3, and the highly exaggerated "sumo" style might be 1:1.
With this thought in mind, if you want the hornbeam to look like an old tree in a field, a 12 inch tall tree would need a 3 inch diameter trunk. 1:4
If you want a forest style maple, a 15 inch tall tree would need a trunk at least an inch and a half, up to maybe 3 inches diameter. 1:10 to 1:5
So measure the diameter of your trunks, make notes, think about what you want. If you need to thicken trunks, don't cut anything.
Well, you can do some, but make a plan first, tell us, we will help you plan out how to get there.