what type of neg. would i take from shooting 2 or more arrows at once?

You can't fire two arrows at once any more than you can wield two swords in one hand.

You can make multiple attacks with a bow in a round, so long as you qualify for making multiple attacks in that round AND the rate of fire your weapon has allows you to make that many attacks. In that case, you suffer the appropriate penalty for the number of attacks you decided on (-25 for both attacks if two, -50 for all three attacks if three, etc).

But you get no benefits from placing a second arrow on the string and firing both at once. If you want to do something like that, look into creating a Ki Technique and talk with your GM.

There is an optionnal rule for that in Dominus Exxet.

- you can string/throw up to 4 arrows/projectiles on a single attack
- declare intent before rolling Initiative
- each projectile after the first gives +10 to Damage, -5 to Attack and -10 to Initiative

Thus, if you shoot 4 arrows at your target, you make 1 roll with +30 Damage, -15 Attack, and -30 Initiative