“My bilingual dad” (with “bilingual” being an attributive adjective rather than a predicative adjective) is mo dhaidí dátheangach. If you wanted a sentence like “My bilingual dad is here”, it would be Tá mo dhaidí dátheangach anseo. It’s the structure of this exercise’s sentence that makes dátheangach in it a predicative adjective rather than an attributive adjective.
I am not great with grammatical terms so don't understand the difference between predictive and attributive adjectives. Could you explain it as if to a child :) I would have used is mo dhaidi datheangach because as a guide I use the spanish Ser and Estar which denotes permanence or transience. I'm thinking now it may not be a good guide.For ex: I would think to say ' Is mo dhaidi albanach' (permanently) and' Ta 'mo dhaidí i hAlban' Where am I going wrong? Any help would be appreciated.
For the difference between an attributive adjective and a predicative adjective, search for “stinky cheese” in this discussion.
Spanish ser vs. estar is a good model for Irish is vs. bí, but one difference in that analogy is that Irish almost always uses bí with predicative adjectives, even if such an adjective represents a permanent characteristic. (See my reply to FoxyAuroraBat below for the few situations in which is would be used.)