DNA sibling-ship tests determine the statistical probability of whether siblings (brothers and sisters) share the same two parents or not. The cost of the DNA testing service includes two siblings, but you may add more as needed.
When the issue of sibling-ship is in question, the recommended method to determine whether individuals are true biological siblings is to test their parents.
In situations where the alleged parents are unavailable for testing, a DNA sibling-ship test can be performed to analyze the relationship of biological siblings. Including one common parent greatly increases the accuracy of this type of analysis and is recommended if at all possible.