Learn English – Phrase or idiom for someone that is overspecialized

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.

Chasing two rabbits from the widely claimed proverb:

"He who chases two rabbits will catch neither."

Betwixt and between

Torn between the two tasks

Stuck in the middle

Double minded from the New Testament:

For he that wavereth is like a wave of the sea driven with the wind and tossed. For let not that man think that he shall receive any thing of the Lord. A double minded man is unstable in all his ways.

Moving farther afield:

Between a Rock and a Hard Place

By implication, Hemming and hawing

Between the Devil and me