I usually use:
Thank you for..
I considered your..
I've seen in my incoming letters:
Diana - thank you..
Dan - I considered your..
So the questions is: What is the right way to write a letter addressed to several recipients?
What your example is showing is a standard way of sending an email to multiple recipients where more than one needs to be specifically communicated to. There is no "right" way to do this as long as each person's section is clearly delineated.