Be wary of drawing conclusions that are not necessarily supported by the evidence. Witnesses to a will only had to be "of age" and able to testify that they saw the testator sign the will. Witnesses to a marriage had to be of age and also be present at the ceremony. While these individuals can be clues, always keep in mind that they only thing you know for certain (or reasonably certain) is that the witness met the legal requirements of being a witness.
Don't ignore the names of witnesses on a document, but don't assume they have to be a relative either.