You say your son asked for the client care partner to be involved. I assume you mean by this that he was making a complaint about the solicitors work, or the fee amount or the insistence on taking your daughter's share of the fee from him (or perhaps all three).
Whichever partner in the firm is reponsible for complaints should reply to this letter and address the issues raised in it. If they don't, or your son is not satisfied, then he can go to the solicitors complaints body. Ring the Law Society to enquire about this.