It's an incredibly tough time. I went though the loss of my dad to cancer just over two months ago. It's shit, and we're a tight family.
Wilkie's right - sort your dad out, and then deal with the family later when things have settled and the grief has lifted a little. If necessary, step in and tell your brother to sort his shit out until, at least, the funeral is over and your dad is learning to cope. Explain that the tone of the email while, perhaps, unintentionally inconsiderate and hurtful, was received that way.
At the moment things are hard for all of us, but my priority is to ensure that my mum is coping. If I fall out with my brothers or in-laws while I'm doing that, so be it. I'll deal with that later.
@Tickled Pink - vouchers are no better than cash. To buy vouchers you take money (that you can spend anywhere) and exchange it for money of the same value that you can spend in limited stores. Vouchers are, on the whole, pointless.
Unless you book as soon as you know you're in, you're screwed. 45,000 runners and their supporters descend on the city that weekend. When I did it I booked a couple of days after getting in (that was in the December before the run) and even then I ended up having to stay in Durham.