Using keyword search, there are 16 mentions of Yan'er*** in the first 80 chapters of the full text. The ten places of the treasure hairpin are respectively at twenty-five, twenty-seven, forty-two and three, forty-eight and two, fifty, fifty-two and fifty-nine. Basically, they are all in conversational form, that is to say, they are addressed face to face. Both locations of Baoyu are in Chapter 30. It's a psychological activity, which means I haven't called him in person. The forty-ninth chapter of Tanchun was told during a conversation with Baoyu, calling Sister Lin "Duo" in person. When Jia Mu was seventy-five, she was giving orders to her servants.
In Dream of Red Mansions, Lin Daiyu should be older than the Sanchun sisters, so the younger ones are definitely not called older. Since Baochai is older, it is reasonable to call him "Ming". Furthermore, this is a word chosen by Baoyu. It is difficult to say whether it counts. The elders may not take it seriously, and it may not be spread only among sisters. Moreover, Daiyu and Baochai are already nicknames, and they are already very affectionate when called by the elders. Although Baoyu gave Daiyu a nickname, it was too outrageous to call him a young lady in ancient times. No one else had the chance to call her, so only Baochai did.
The frown is taken from Baoyu (Cao Xueqin)'s praise of Daiyu's beauty, which alludes to Xue Baochai's brother Xue Pan's love for Lin Daiyu, and his concubines Xiangling and Xia Jingui are related to "Dong Shi Xiaofeng". Xue Pan married Xia Jingui because Xue Pan heard that the daughter of the Xia family was well-educated and could write poems, and she was beautiful, so he begged her to marry her. (Of course it was because he admired Daiyu but couldn't get her, but still wanted "the same style". Who would have expected that Xia Jingui was not at all what Xue Pan imagined).
So the overlapping character "馢馦" means "二". Since it is a name with specific meaning, naturally the author will not let everyone call Daiyu Finch, Finger, Sister Fong, Yatou, Miss Fong, etc. all the time. So it is naturally the author's interest to arrange for Baochai to be called Qian'er, and this name is just related to the Xue family.