Congrats - truly once in a lifetime! But on the issue of taxes, you'd definitely better find out because YOU'RE the one who'll have to pay the taxes, I don't think your friends coming along will. I certainly don't want to rain on your parade, but a 2 week, all-expenses paid trip for 10 or 11 people to Africa has got to cost at least $5,000 per person, or $50,000 - just an educated guess. If it does, you'll probably owe over $10,000 in taxes on it, so I'd suggest you ask each of your friends to chip in 1/10th (or 1/11th) of the taxes due so you don't take the entire hit.
That said, best of luck to you :cheers: