So I installed double helix tethered jailbreak on my 10.3.3 iPad mini one month ago. But now the JB apps, cydia and games crash whenever I try to open them. Also there is no option to delete cydia and other apps. How to delete these?
There is never an option to delete Cydia.
If you want to delete Cydia it implies you want to remove your jailbreak. Since Cydia allows you to install JB tweaks and apps there is no point in deleting it and remaining jailbroken unless you intend to do any tweak installing in some other more difficult way.
So, I am going to assume you want to remove your jailbreak (which will remove Cydia).
1. Backup, either to iCloud or iTunes. I'd use iTunes if you want to retain everything including passwords.
2. Sign out of iCloud and all services requiring an Apple ID (Facetime, iMessages, App store, etc)
3. Turn off iPhone.
4. Connect iPhone to computer that has latest version of iTunes.
5. Open iTunes.
6. Put iPhone in DFU Mode (Google it, it's out there). Doing this will turn the iPhone on. You are properly in DFU Mode when the end result is a blank screen.
7. iTunes will detect an iPhone in recover mode.
8. Upgrade and restore as new through iTunes.
9. When done, use iTunes (or iCloud) to restore from your backup.
The jailbreak will be completely wiped and Cydia will be gone.