There is no reason why they can't. It is simply a matter of having the two samples tested using the same methods. The results should be able to determine the level of relationship.
because
Same father (half sibling)
The children are both your cousins[uncle's children]and your nephew and niece[sister's children].
If your half-brother has a full sister, she is your half sister. If your half brother has a half sister, she may be your full sister, or she may not be related to you at all.
She has 1 sister, a step-sister, a step-brother, a half-sister and a half-brother
If your brother-in-law is the husband of your sister, presumably his daughter is your sister's daughter, too. Then his daughter and your nephew are either brother and sister or first cousins. If the daughter is not your sister's daughter, but the child of a previous marriage, then she is could be the half-sister of your nephew or not related to your nephew at all. If your brother-in-law is the brother of your spouse, then his daughter is your niece and your niece and your nephew are either siblings, first cousins, or not related at all, depending on how your nephew is related to you.
Helen Keller had two half-brothers from her father’s previous marriage who were also her first cousins. Their names were James Keller and William Simpson Keller.
yes i know for a fact he has a half brother and sister
It is your sister's or brother's son, your adopted sister's or brother's son or your half sister's or brother's son. That would make you an aunt or uncle.
Your half-brother's half-sister could be your full sister, or not related to you at all. For example, say your parents are Joe and Mary and your half-brother's parents are Mary and Steven. Say your half-brother's half-sister is Barbara. If Joe and Mary are Barbara's parents, then she is your full sister and your half-brother's half-sister. If Barbara's parents are Steven and Jane, then Barbara is not related to you (unless there is an adoption).
In Spanish, "half brother" is "medio hermano" and "half sister" is "media hermana".
A sibling is any person who is either brother or sister to that person. Half siblings and step-siblings are the same, are the same, but half sibling is a half-brother or half sister, and a step sibling is a step brother or step sister. No matter what your age, any brother or sister is considered a sibling.