If you do nothing:
If you both die, the money will revert to your estate, and follow the directions in your will. This is not terrible, but may end up with some estate tax or probate fees which are pretty small, overall, right now, on the average estate. The money will be distributed to the trusts you have set up in your will, per your will directions.
If you name your daughter, and she is a minor:
If you both die, it will bypass your estate (will) document, and the state will have to set up a trust and trustee to administer it until age of majority. Usually the trustee is someone like a lawyer for the state, who gets paid from the trust. This option is very expensive compared to the others, and you are better off with do nothing. (If you are already paying for a trust, with your will instructions, you do not want to pay for yet another, more expensive trust management fee with the state's instructions only on it).
If you name the trust you have set up:
This is the one where you need to know what will happen if you name an intestate trust as a beneficiary, that has not been set up until you die. Here (my region), the money would go to the trust named on your retirement account, as the trust set up in your will would be presumed to be set up first. If you have a living trust (while you are alive) pre-setup, there is no question. The money goes to the trust.
If it is not considered to be set up when the money transfers, then it bounces (as if you tried to give money to a deceased person), and it goes to your estate and your will to determine how it is handled. (like the do nothing option). Here, this is your best option.
If you give it to your brother:
No problem here, but he can use it however he wants. If you trust him, great, but why would you have set up a trust in your will if you felt this way? In your will you would have just given it all to him directly and saved the trust hassle.*
*Trust hassle -- the effort and additional cost to get a lawyer to set it up in your wills, and the set up cost of the actual trust at that time, and the hassle of providing specific instructions on how you want the money invested or distributed after your pass. Obviously there are tax and distribution control benefits that come with a trust if you are putting a large sum of money into it.
Contingent Beneficiary:
Ask your retirement plan provider how they want the contingent beneficiaries worded. Some have automated systems that do not provide for contingent beneficiaries in the database, but you can provide a written, witnessed letter describing your intent -- "100% to my spouse, and if he is no longer living, 100% to the trust XXX"..
Age of majority: As soon as your daughter gets to the age of majority, where you want the funds directly to her, change your beneficiary designations.