Well, for the first part of your code, you can do this:
(set: $result1 to (random: 1,6)+(random: 1,6))
(if: $result1 is 7 or it is 11)[Uh, it seems you got a point?]
(else-if: $result1 is 2 or it is 3 or it is 12)[Looks like you've lost given by their sly grins]
(else-if: ($result1 >= 4 and it <= 6) or (it >= 8 and it <= 10))[Point? No? I don't know. Could be a tie.](show:?cloaked)
|cloaked)[Do you want to roll again?
Yeah or nah?]
You can set $result1's value to be a sum of two random rolls (unless you want to use $diceroll as a variable somewhere else, in which case your code is right).
The (show:?cloaked) macro will hide the "try again" session until the player rolled.
For the next part, I'm sorry, I could not figure out how hide the Nah button. You can link the "Yeah" word back to the dice passage, and put the whole try again session into an (if: ) that will prevent the player to try a third time. Like this:
(if: $tryagain is true)[(set: $tryagain to false)Try again? [[Yeah]] or [[Nah]]?](else:)[You already tried twice!]
I hope this helps a little bit.