In Illunse, pronounce au as in how or owl. This is as in Latin. Old English doesn't use au as a diphthong.
In Illunse, pronounce ae as in cat. This is like æ in Old English, the grapheme formed from the letters a and e which is a letter called æsc ("ash tree") in the Old English alphabet. It's unlike Latin in which æ is a ligature representing the Latin diphthong pronounced like ai in aisle.
I decided on these pronunciations for Illunse quite a while ago. These are certain, they won't change.