I think the twins were 21st level, maybe 22nd when we started this weekend. They're about halfway through level 26 now. Keep in mind that this is Warren's first time through any of these quests, and he likes to take things slow, enjoy the scenery, roleplay, and talk (in character) to random folks. He also spends a lot more time than normal running city errands because he wants to think through his training and profession and stuff. Also, the twins are entirely untwinked. I know that for hard-core power gamers four or five levels in a weekend might not be a big deal, but for us its pretty darn impressive.
I guess the major milestones for the twins were there first real foray's into non-elf lands, and the first time they'd been in a dungeon. The twins had been to the Wetlands a little bit before, but hadn't done more than a couple of quests there. Yesterday, though, they to Stormwind. They also went to Theramore, and travel through the marsh lands and then through the Barrens to Thousand Needles for a quest involving Highperch wyverns. They also got to the little elf area on the eastern edge of Ferelas. Saturday was their first time in an 'instance'. They went to Blackfathoms Deep, and ended up teaming up with another hunter we knew who we just happened to run into outside. We didn't get anywhere close to all the way through; we ran out of arrows! (I have another hunter character, but she's not done an instance yet, so I had no clue how fast they ate up ammo.) We did get two of the quests done, though. We'll need to go back and deal with the Twilight Cultists.
From a player psychological prespective this weekend and past week also marked a bit of a shift. My "main" character is now my half of the twins. Two of my alts are still higher level, and I plan to continue playing them when Warren isn't available, but they're now second choice. We only play the twins when we can play together except for running character errands. I figured out the thing about who my main now was when I logged in as her on Sunday morning and spent nearly an hour fishing in Menethal Harbor before Warren woke up instead of logging in as another character and questing.