Oh cool, I actually didn't know that! Just delete that part for Simon and all is well ^_^

And I like to mention that Simon is not blind is his left eye. He has both of his eyes. Only Sigmund is blind in his right eye. It is mentioned in the BloodRayne Wiki

OH and the Mynce achievement should be before the two brothers achievements since you're doing chronological order

Sry for the spam, but the character limit didn't allow me to post all of it ^_^ hope I didnt make any mistakes as well ;p

Strategy - This is a special type of gun which can be obtained in the final fight when you face Beliar and Wulf. When the fight starts, go upstairs. Go to a pillar and jump so that you are on the outside edge of it. Jump up and turn around. Now you can see some cages that are hanging from the ceiling of the dome. Shoot all of them down. Now jump up to an even higher ledge (you need to do a backwards jump to reach that ledge, if you do a normal jump the ceiling will block you). Once you reach the highest ledge you will be given the 'Head Guns'.
If you do this correctly, two head shaped guns will appear in your weapon slots.

And you don't need an empty weapons slot to acquire them, they will replace some existing guns in your inventory.

Strategy - You should target Beliar first. To take him down you have to target his weakest point - his heart. Shoot near around his chest and he should go down pretty quickly. If you have the rocket launcher, you can take down Beliar with around 3-4 rockets aimed at his heart.
Wulf is fast and you have to keep up with him. To take down Wulf just activate your Rage and he should go down pretty easily. I would avoid using guns on Wulf as they do very low damage.
Note that you CAN take down Wulf before Beliar, but you have to do it BEFORE Beliar becomes too big and tears down the roof.

Strategy - This is in the level where you are tasked with destroying the communications of the GGG. When you reach this level a cut scene will play where a general goes down an elevator/lift and a soldier that runs off with the battery. Jump a floor down, turn around and go through the door. Upon entering there will be a single wooden box. Destroy the box and the Ark of the Covenant will be revealed.

Additionally, I'd put the Ark achievement before the Von Blut achievement, because the level with the Ark is just before the chapel fight.

Strategy - Simon is blind in his left eye. It's hard to know which one is Simon once the battle starts. But on the bottom-left, where it shows the HP of both of the brothers, Simon's HP level will be on the bottom. After you have defeated Simon first, Sigmund will commit suicide right after.

(there is no need to mention Rayne's HP, everyone knows whatya talking about :) )

Strategy - The fight is divided into two parts. The first part happens on the stairs. Here you cant completely kill her, because after reaching a certain HP point Mynce will stop fighting you and run up the stairs. Then you just follow her up to the top. The second part starts when Mynce reaches the top and the door closes behind you. Here you can defeat her easily.

Thanks for the guide! Here are some corrections:

This is the very first level where you are given control of Rayne. As Mynce goes inside the Chapel, go outside and jump up to the roof of the Chapel where there will be a cross. That is what you need to destroy.

For the butchress you need to put a space between "up" and "to".

Strategy - You can exploit his slow speed to get some hits in and then back off to build up your Rage. Once you have your Rage meter full, activate it and you can get him to low health pretty easily. But beware as even in Rage mode Mauler can you hurt you.
Here also some guards will be spawning regularly, you can use them to get your health back.

Strategy - Sigmund is blind in his right eye. It's hard to know which one is Sigmund once the battle starts. But on the bottom-left, where it shows the HP of both of the brothers, Sigmund's HP level will be on the top. After you have defeated Sigmund first, Simon will commit suicide right after.