I do this for a living, and can tell you that I can count on my hands the number of clients who are my friends. Not so much because they don't trust my judgment, I'm sure, but because most people don't like others close to them to find out how much money they have (or don't have).
Now- that does not mean you shouldn't use your brother. In tough times like these, clients are hard to come by, and I'm sure he could use the commission/production credit.
And- by being a family member, he isn't going to steer you wrong, especially if you are putting money into highly secure places. This is important because some advisers might have you put your money in something that is not the best for you simply because they'll make more off the deal. I just can't see a family member taking advantage of you that way.
The biggest questions for me are these:
1) Do you mind your brother knowing how much money you have?
2) Is your brother qualified to help you decide where you want your investment?
If you answer no and yes, then why not?
If you are tuly putting money in a safe investment, and the market goes so bad that you lose money- I mean, the last place to put blame would be your brother, wouldn't it?
If the relationship goes sour, you can always move the money.
For me, good relations can go sour with anyone, not just family members, so if that is the hangup, keep that in mind.
I edited to add this point...the investments I will be putting the money in will be liquid and very secure, so I'm not at all worried about tensions from him making bad investment decisions and losing a portion of my money. I will be putting the money in very low-risk investments as I will need this money about 4 years from now. I guess this leaves me with the only potential tension or akwardness coming from him knowing my financial position, and maybe even jealousy, which I don't foresee. Thoughts?
Reading this again and knowing what is out there as far as investments go- I really don't see how he could mess things up for you. We can narrow the amount of highly liquid short term investments down to just a few things, none of which could put you in worse shape financially.