〜が〜なら

if A is like that, (no wonder B is too)

Noun A が Noun A なら、Noun B も Noun B だ

AがAなら、BもBだ says that A and B are as bad as each other: 親が親なら、子も子だ, "like parent, like child", said critically.

A and B are a related pair: parent and child, boss and staff, shop and customer, husband and wife, teacher and student. Repeating each noun means "the kind of X they are". The tone is always disapproving: both sides are to blame.

It's a fixed rhetorical pattern, common in conversation, gossip and TV dramas, and you can't make it positive.

Compare the proverb あの親にしてこの子あり (N1's にして), which can be either admiring or critical.

Examples

親おやが親おやなら、子こも子こだ。
Like parent, like child.
上司じょうしが上司じょうしなら、部下ぶかも部下ぶかだ。
The boss is bad, and his staff are no better.
店みせが店みせなら、客きゃくも客きゃくだ。
The shop is dodgy, and the customers are just as bad.
夫おっとが夫おっとなら、妻つまも妻つまだ。
The husband is bad, and the wife is no better.
先生せんせいが先生せんせいなら、生徒せいとも生徒せいとだ。
The teacher is hopeless, and so are the students.