I'd say a mix of the two builds is in order: Ranger 6/Scout 4/Dervish 10 using Swift Hunter. You can still mostly dump Dex (you need a 13, or 15 to take Two-weapon Rend) and pump strength. You don't get to take GTWF without a huge dex that will be a waste, but 6 attacks per round at max level (doubled to 12, once per day) is still pretty impressive.

The big thing with TWF, especially in a party like this one, is that if he can't get his full attack in, he is just way worse than everyone else, and even with his full attack, he is going to be behind the barbarian in terms of accuracy and damage even with his extra attacks per round. Using Swift Hunter remedies this by adding precision damage (Skirmish dice) to all his attacks, and Dervish remedies this by allowing him to "Dervish Dance", gaining a full attack + the ability to move away while TWF. He can also be a decent "tank": he has above-average saves for a front-liner, and has monster AC if he uses the Dervish Parry + Combat Expertise, + armor from Dodge and Skirmish, which makes up for his smaller health bar (as compared to the Barbarian).

So Dervish is almost a necessity, and if he can't have it, then having some way to move and full attack (Travel Devotion, Pounce, Belt of Battle) is going to be required.