Caller ID (which includes the SMS sender field) is spoofable by design. I'm fairly certain the numbers you have are innocent people's numbers chosen at random, and the offensive texts were actually sent through an online SMS service.
In any case, your mobile carrier may still have the logs containing which carrier the texts really originated. It may end up nowhere (if the far-end carrier is an online SMS gateway and the attackers used Tor, proxies or compromised computers to conceal their identity) but it's worth a try.
Get in touch with the police, they will obtain the logs from your phone's carrier and investigate based on that, and they may be able to locate the attackers, but as I said, if the attackers did their job right, the chances of them being brought to justice are unfortunately close to zero. Your best bet is to ignore them, possibly change phone numbers & e-mail addresses and making sure none of your new information leaks out (don't reveal too much on social networks, etc). Google your name and your relatives and see what comes up. Try to get any personal information taken down or change it so whatever data is published is no longer valid. I suggest you read this : After getting doxxed, how can one protect personally identifiable information?
I doubt your iPhone was compromised, especially if it's up to date. iOS exploits retail for millions on the black market and I do not think someone would waste valuable exploits just to bully someone. Your computer, on the other hand, may have been compromised. I suggest you reinstall it and change your passwords.