What Is Wrong With My Younger Cat!

So the other day my brother came over to help me with something on my computer. When he was done he was waiting for our mom to come pick him back up and Tikki rushed over to him and meowing.

He reached down and got two strokes off before she hissed and slapped at him. This is where it gets weird, she continued to rub on him and reach for his hand to pet her, but she was also hissing and slapping at him. Why was she acting like this?

Tikki was a front of the yard rescue and she was already 3 or so months old when I caught her. I heard that cats that are domesticated late don't really bond with anyone else except those that domesticated her. But she's also started slapping at my father when he visits and has also started exhibiting weird behavior with me too. She used to be so loving, but now she'll run up for me to pay attention to her, then run away or slap at me when I try to pet her.

Tikki is six. She also attacks my older cat for no reason. She will jump on him and then automatically hiss and spit even before he turns to do anything about it. I'm not sure what to do with her. I've tried playing with her, but she is never interested. I'm a little frustrated with her and I'm not sure what to do about it.