As the others have said, I too am truly sorry for your loss of your brother. Its a tough hit and the prolonged battle with cancer just makes things seem bleaker. From personal experience I can tell you that depression is a very real and painful, debilitating thing to have. I'll throw my hat in with those that said to try riding anyway. No pressure rides with no real aim or goal other than getting out in the fresh air and expending some energy can be a true head clearing time for me. Riding a bicycle has saved me from even worse depression over the last few years, probably kept me from doing something really horrible and irreversible to myself for that fact.
I'll have you in my prayers for strength and recovery, keep things in perspective, remember that your daughter needs you now, even if she hasn't said anything about it. I hope things look brighter for you soon.
Bill