HELP! House hacking with BAD contractor

[Nora Douglas]

I bought a 6 bedroom property 10 years ago, cash. Have been renting out the 3 extra rooms for the past 3 years and saved up enough to get a new roof. Contractor did a bad job.
I found someone to fix the job for cheap, but CAN I SUE THIS CONTRACTOR?

Some details about said contractor: 

- Contract was signed, digitally 
- Work was quoted at (a super cheap, I now know,) $4000.
- This contractor is my sister's boyfriend's grandpa and said boyfriend lives in my house
- I want to take them to small claims court but not sure if its worth the hassle 

Would appreciate any guidance, THANKS!!