Blood of the Dead: The clan is able to manipulate the blood of the recently dead without the need of Medical Ninjutsu. They can create a Catalyst Item known as Blood Chalk, which allows them to store ninjutsu in symbols drawn with it without requiring the use of Fūinjutsu. They also can create specialized traps using fuinjutsu and writing special circles in blood chalk. Blood chalk is a special fuinjutsu in which they seal the blood of the dead with the user’s chakra into chalk. They have the ability to create the blood chalk by spending one post over a dead person's body or over the bodies of animals with the equivalent size to a human (say 6 rabbits or 1 deer). The blood chalk is dangerous to touch for anyone outside the creator of the blood chalk.
This is fine, since it is simply a tool that lets you do jutsu with blood. Once the kkg is approved, i would app the blood chalk as an item, and each clan member gets their own.
Limits to the summoning are as follows. 1 wraith is equal to 4 skeletons
C Rank: 2 Skeletons
B Rank: 4 skeletons
A Rank: 8 Skeletons
S Rank: 16 Skeletons (The ability to summon the most powerful wraith becomes accessible at this rank but a special ritual must be performed and permission granted.)
These numbers are way to strong, you are essentially getting access to another body, even at S rank summoners do not get this many bodies. i would bump these to 1,2,3 and 4, for C,B,A and then S.
When first mastering the summoning, the skeletons will attack everyone and everything. As most users do not begin training until they are between ages 10-12, this can cause significant problems when trying to use their special summoning jutsu in a team setting. Only a properly crafted circle of cerberus will keep them at bay until the proper training has been achieved. This takes about ten years. For example, Karite started her training at 6 and was a danger during training until she was seventeen years old. When she was ten, she accidentally stepped on the circle and messed it up, causing the skeleton to break and attack her. Now she is able to keep the circle of cerberus on her glove as proof of her strength.
While it is ok to keep this flavor in, it is not a weakness. You basically circumvent the weakness with your history or just being an older character. It does not inhibit you in anyway.
Going to need 2 more weakness's
The skeletons have a weakness of lightning ninjutsu.
This is ok, but detail a little more on how a skeleton can be killed.