when u say [εə], u pronounce it with rolling back ur middle tongue little bit. Meanwhile [iə] is simply pronounced [i] and [ə] but u say it as diphthong and lightly. to listen accurate pronunciation of every word, u can download Cambridge or oxford electronic dictionary please kindly to contact me if u have any question. hope it give lil bit enlightenment

You should put some ice on your tongue while trying to pronounce such words. You can also try to stretch your tongue every morning. Hope this helps.