After a bit of consideration, I'd say starting attack should be adjusted downward. The twins already possess three combat advantages over a starting Hero. First, they may each attack once as a starting Hero. That amounts to an extra attack over a single Hero. Second, they may combine for a heavy attack against a single opponent that outshines a starting Barbarian. Third, they can often focus defense on the only twin vulnerable to a counter attack. On top of all that, they also get an extra search or possibly disarm action. That can result in twice the treasure of other Heroes.
For those reasons, I'd reduce the twins' starting attack to 1/1. Maybe the starting weapon should just be that special, reusable dagger for each twin. I say this with the understanding that they would be allowed to purchase equipment as I've suggested in the previous post.
I also would like to see only 1 Defend and movement die shared (assuming equipment may be bought.) Otherwise a twin in combat could roll 7 or 8 Defend Dice with his/her partner safely out of harm's way. So here's an amended version of the ability:
If the Twins have line of sight to each other, up to one attack, one defend, and one movement die may be donated to the other Twin as you choose for one turn.
With equipment purchases this is quite strong, so I'd simplify and go with this:
If the Twins attack the same Monster, up to one Attack Die and one Defend Die may be donated to the other Twin for one turn.
The Twins work together as a combat team, but movement isn't affected because. . . how? And I'd even recommend dropping the throw ability. A bonus attack, combat dice perks, and a bonus search action are already stacking this Hero-pair above the basic four Heroes quite a bit. If you are creating your other Heroes at a more powerful level and increasing the difficulty of your Quests (or not allowing equipment to be purchased), then keep the throw ability. More power to ya!