Nobody here has mentioned a bad knife.
One question that comes to mind is how the individuals involved would use the knife? Are they ranch hands or bankers?
For a gentleman's gift knife near the stated $150 mark, I think it would be REAL hard to beat William Henry's offerings. Especially one of the T10 variants. I have a CF version but really have the hots for the Black Diamond blade Executive version of that same knife with the gold trim. It's really sweet.
If they're more rough and tumble sort of guys, the Benchmade 705 mentioned would be a great choice but I find it a little too industrial.
I think the Benchmade 940 series is probably the best all around design for the money in a folder that size. It can almost be a gentleman's knife and almost be a ranch hand's knife at the same time. I like it enough that I have four copies of the 941 version. With this knife you can also choose from a wide variety of blade choices. A cool thing to do might be get Dad a Limited Edition one (there's a couple different ones) and get the brothers a regular production version (still really great knives). The Red handled LE with the BC1 coated 154 CM blade is very cool, but to me the Carbon Fiber LE with the mirror polished D2 blade is the top of that class (and I have at least one of each).
All that being said, If you have the bread to bestow Chris Reeves knives on your family members, it's well worth the extra cash in my opinion. If you went the Sebenza route plain small ones would probably be the choice as decorated ones would raise the price even higher ($450- $600 ea. You would be giving them each a knife that should last a lifetime (albeit sort of plain looking in undecorated form(what i have)). If the guys in question would do better with a subtler, gentleman's style knife but you'd still like to step up to Chris Reeves quality, then the Mnandi would be a perfect choice. They are beyond sweet (haven't got one of them yet).
To toss out one more option and confuse you further, think about the Microtech Mini Socom. Those can be had online in your price range and would present something a little rarer than a Benchmade with tremendous fit and finish. Microtechs are simply awesome knives. I've also seen automatic Mini UDTs in your price range if you wanted to give them something a little more controversial. The blades are just over 2" on the Mini UDT.
As mentioned, these are my opinions.
jmx