I appreciate your comment but I am very careful to make sure that I'm not adding people for whom I don't have complete confirmation, including, as you point out, different names for the same people. It is precisely the lack of care you point out that makes using other people's trees a dicey source of information in my experience.
And another point to add to yours is that the relationships are not necessarily what they are stated on forms or what they might be thought to be at first. Sisters appear to be wives etc. So, I agree about the cautions!