Nancy, I would stick with autosomal tests. Remember that for testing to work, you have to have others tested too, and be able to compare with them. If the brothers take a test that no one else has taken, they can't compare. All they can do is learn what broad yDNA haplogroup they are, and gain some knowledge of their STR values, which may be useful *someday*, when someone else related to them has tested. Also, yDNA is more useful for deep ancestry, almost never useful for matching someone. It can almost never determine precise relationships, just inform you (once both have taken the more expensive yDNA tests) if you share a male relationship, through fathers, their brothers, their grandfathers and grand uncles, etc. The one thing it's very good at is to *reject* a potential relationship - if their high level yDNA haplogroups don't match, then they aren't related within tens of thousands of years (at least not through the paternal line).
Autosomal tests are very good when it comes to close relationships. The closer the relationship the better the confirmation that a DNA test can provide. And you already have autosomal tests for comparison with others. Plus, it's much cheaper to get others to take an autosomal test, especially if you or they buy them during the annual DNA test sales.
It's true that FamilyTree DNA provides the most complete set of yDNA tests, but you can also get a fairly good yDNA haplogroup from both the 23&Me test and the Living DNA tests. Their tests cost a few bucks more, but they include autosomal, mitochondrial, and Y chromosome tests if you're a male, in one package.