Welcome to Ireland Reaching Out!
I see from the marriage record that John and Elizabeth were Church of Ireland. The subscription site Roots Ireland has baptismal records for Stranorlar parish back to 1802. However, there were no baptismal records for John and Elizabeth in that parish on Roots. Also, did not find a record for Aaron Hastings.
I checked the 1830 Tithe listings for Stranorlar civil parish. I located two Hastings records including a John. The townland was shown as Danwilley which would be Dunwiley today. Likely this John is your ancestor.