Like I said, if you do need to surmount obstacles of any kind, practice, practice, practice. Remember you are now responsible not only for yourself if you end up laying on the ground, but your stoker who has extremely little control over the situation will end up laying on the ground and because it is likely to be more of a surprise to her (or him) they often come out with more injuries from what I have read.
Was going to post about the chainrings... Remember simple trigonometry, even though the bottom of the tandem is higher than on a single, it is higher because the length of the tandem will make it more likely to "straddle" an obstacle when you go over it. Would be a big problem to try to surmount the curb and end up with a wrecked chainring. (Reference the above about falling down if you suddenly hit the curb with the chainring...)
OK, maybe I'm a wimp, but I stop the tandem, we dismount, and I walk it over obstacles the size of curbs. We have a lesuire bike (Trek T900) not a mountain bike.