If the oldest is disappointed he did not get a 7, teach him that one needs different knives for different purposes, a bigger one and a smaller one.
That every guy needs a knife like the 16, also Ethan loves the 16, that'll go far.
That will also let him anticipate his larger knife someday, will it be a 7 also, or maybe a 9?
A 15 yr old can mow lawns or shovel snow for knife money, good character builder. He can then get whichever one he wants, and it also will mean a lot to him because he earned it. His dad gave him one, and it's his first, so it's special.
The bigger one he worked for, and it's his "big" knife, so it will be special, too.
I used to make hay for a measly $1 an hour, hard work but it added up and there was no other way to make $$ growing up where I did on a farm. I upgraded from JC Penney "Plainpocket" jeans to actual Levi-brand jeans, like everyone cool wore, and 38 years later it still was the right decision. I paid the difference in price when we bought school clothes every year.