Park Dong-ik only notes how the father stinks and not the rest of the Kim family.
Because the smell isn't that strong and Mr. Kim is the only family member that Mr. Park shared a car with.
Mr. Park sits just behind Kim Ki-Taek every single day and the vehicle they're in has a fairly small cabin with no divider between them. When speaking to his wife, Mr. Kim describes Mr. Kim's smell as subtle and slow to notice. From the script --
DONG-IK: Hold on, I know that smell. (sniffs) This is Mr. Kim's smell.
YON-KYO: Mr. Kim? Are you sure? (sniffs) I don’t know what you’re talking about.
DONG-IK: I guess you don’t know. I sit behind him every day so I know the smell.
DONG-IK: It’s not that strong. It’s more like a subtle aroma that seeps into the air -- it just creeps into the backseat and surrounds you.
Since Mr. Park is never so close to any other Kim family members for an extended amount of time, and whenever his is around them they're in open spaces, Mr. Park never detects the smell on the rest of them.
This question assumes that the other Kim family members even have the same smell on their clothes/body to begin with. It's entirely possible that the other family members take different routes or methods of transportation around town, and/or Mr. Kim's clothes are much older than his children's (and therefore have acquired a kind of muskiness over the years).
The only similarity in smell that was mentioned between the Kim family members was when Da-Song noted that Mr. and Mrs. Kim smell the same due to using the same laundry detergent.