In South Carolina deadly force may be used to prevent harm, if one deem it necessary to prevent harm. There must be a reasonable fear of immediate danger for this to apply. This applies to defending someone else.
To prevent trespassing one only needs to convey that the way they dealt with the trespasser was appropriate.
+Q: Does South Carolina have a "stand-your-ground" law?
+Q: Does South Carolina uphold a peaceable journey?
+Q: Does South Carolina have restrictions on assault weapons?
+Q: What NFA restrictions does South Carolina have?