Here are my corrections:
5. If it doesnít rain, we could go swimming.
8. If you found (find) a skeleton in the cellar, wouldnít talk (talk-neg) about it.
11. If you left (leave) your purse lying around, it would steal (steal)
12. We had to (must) to walk if we would run (run) out of petrol.
14. I would answer (answer) the phone if I knew (know) it was you.
Student or Learner