I'd suggest reading through this thread: http://community.fan...on-about-dodge/
The Genestealer is used as an example there, so its abilities are covered in details in the second half. But to recap:
1) Lightning Attack: In short, as a full action, you may make 3 attacks. But here comes the important part: If the character has the Two-Weapon Wielder Talent and is wielding two melee weapons, the character gains the advantage of Lightning Attack with only one of the weapons, and a single attack with the other. That's 4 attacks so far.
2) Ambidextrous: The talent doesn't give more attack opportunities, it just means you can lessen the penalty: When combined with a Two-Weapon Wielder Talent, the penalty for making attacks with both weapons in the same turn drops to –10
3) Two-Weapon Wielder: You could use a Full Action to make two attacks at -20. However, the description of both Lightning Attack and Ambidextrous specifically states the effect when combined with Two-Weapon Wielder, so it doesn't automatically stack up with those effects.
So, all in all, in standard laboratory conditions, the Genestealer may use a Full Action to attack four times, with a -10 penalty to each attack.
If there's an incorrect interpretation, please correct it, but basically that's the Standard Issue DW Genestealer righ up there. If you involve crunch from the other FFG 40K games, it might change drastically, but that's uncharted territory for me