Half siblings having a hard time, keep showing under the wrong parents and not as my sibling's.
You add your birth parents as married to each of their separate spouses, if that is applicable, and then add yourself to the 4 parents as a child. Make sure to edit the relationships so that biological relationship is correctly set and "step" is also set. Step is highly inappropriate for this, but it is the best option in the drop down list. Then when you add the children from each marriage you will be able to see your maternal half siblings as separate from your paternal half siblings. I would also think about adding your adoptive parents, if that is appropriate to you. Then you would also be able to see your adoptive siblings.
I have an adopted relative who has the 3 sets of parents such as I described above. It works very well for the family and helps me (the family historian) to keep things organized as well.
You don't mention whether when adding half siblings if you are using the website or the app or if you are trying to add them on a person page or a pedigree page. I find it most straightforward and least confusing to use the website in the left hand column of Family Members section on the Details tab of the Person page. If someone has children with more than one spouse, you can clearly see which couple relationship the children are being added to. Here in this example, there are three choices for adding a child: the first couple relationship, the second couple relationship, or a new couple relationship:
As with so many things in Family Tree, there are multiple ways to add children so find the one that works best for you. As I said, I like this method because you can see the entire family structure at the same time and see exactly where the child is going to end up.