I don't quite understand what your asking. Cant you just answer them like
@B: this is a response to your question
@C: this is a response to your question
@D: this is a response to your question
Then the readers can easily see which part of your post is theirs.
Many experienced forum users do this, so I dont see how this is something to be expected. If you want to multiquote, just quote the last message, we dont need to be seeing the first post 10 times in a nested quoting quote.