This is the opening statement of our parent letter:
"Welcome to ___ grade! Our names our _______ and ______ and we will be your child's teachers this year. We team teach in an inclusive classroom which means that your child will have two licensed teachers in the classroom for most of the day. The extra support is a benefit for all students."
The rest of our letter continues like a normal letter with updates on what we both did over the summer, what we're looking forward to, expectations, contact information, etc.
That's really all we put in the letter. We have a few questions at the "Welcome Back" night but mostly the parents are accepting of it without questioning. We'll get a few "So who's the real teacher?" and we just explain that, yes, we truly do have two teachers who are able to team together to meet the needs of struggling learners as well as challenge the students who need a challenge. That way the parents realize that the benefit isn't only for students who have disabilities or are struggling learners. Almost all of the parents talk about how relieved they are to have extra support in the classroom and see the benefit right away. The only time we really clarify that I am the Sped teacher is that I mention to the parents of the students with IEPs that I will be the case manager this year so they can make that connection.
Your letter may depend on how your model is set up. With our model, we really both share both roles so we don't point out who is who. Just make sure that you are both comfortable with the wording of whatever goes home.
Hope this helps! Good luck! If you have any other questions let me know!