How do I fire my boyfriend's uncle?

My brother in law and sister let me move into their house when they moved to another state for the military. In exchange, he put me in charge of finishing the basement here in Colorado. My boyfriend's hippie uncle just got out of prison and was having a hard time finding a job, and claimed to have 15 years of experience in construction, and he said he'd do the job for only $20 an hour plus materials. When he did the shower, some tiles were crooked and he got cement on the the walls. When he put in doors, they didn't shut right and I had to sand them, and he chipped parts of the frame. When he did the trim, he put little cracks in the drywall, and he put trim in a part I told him not to put trim on yet. I really don't want him working on my sister's basement anymore, but I don't want to be mean, and I don't want my boyfriend's family to be mad at me.