Learn English – Phrase or idiom for mentioning an idea/topic the other then can’t stop thinking about

If you want to convey the idea of someone's who makes the final decision, whose word is respected and whose opinion is never disputed, consider the following options.

• He who must be obeyed. Better known as she who must be obeyed. Its meaning is self explanatory and in the OP's context this phrase might be said in all seriousness or in a lighter, more humorous tone of voice.
• He's the boss. Not exactly an idiom but it implies that you don't mess around with this person and whatever decision he makes is final. A related idiom is show somebody who's boss

We had had a special respect for my father in my family and his

opinions and ideas were always accepted by other family members and as they put it, he was the boss.

• His word is law. There's no use questioning any of his rules - his word is law around here.

• Say-so. Usually a permission or instruction to do something given by a figure of authority. Nothing happens without his say-so.

and as they put it, nothing was decided without his say-so

• Have the final say. In many families, the mother has the last say on the children's education and activities.

...We had had a special respect for my father in my family and his opinions and ideas were always accepted by other family members and as they put it, he had the final say.

"By the stars" would not necessarily suggest that the speaker has no idea. It sounds more similar to "By Jov" or "Oh my God" which can suggest a pretty wide array of reactions, from surprise and bewilderment to outrage. Also, using it the way you want to can even come across as a type of truism, since the general meaning of the sentence it will be used in is that the speaker has no clue, so there is no need to use it both as an opening line and then reiterate it several words later.

"By the stars" is a nice choice of idiom to express the speaker's surprise, so you can keep using it, as long as you agree to let go of the intended meaning of "I don't have the faintest idea". It just makes the sentence it's used in sound needlessly convoluted and there's a very good chance that your readers will not understand it the same way you intended it.