Hello and welcome to JustAnswer. Please note:This is general information for educational purposes only and is not legal advice. No specific course of action is proposed herein, and no attorney-client relationship or privilege is formed by speaking to an expert on this site. By continuing, you confirm that you understand and agree to these terms.
I am sorry to hear about this situation. Yes, if there is a threat to take custody, it is recommended to use counsel to write a letter back.
Why? Understand the following:
1) A letter is just that - a letter. It is not a legal filing and in the end, this is just a correspondence between parties.
2) However an attorney's letter threatening litigation, and that their client would also demand attorney fees "when they win" may scare the other party and have them reconsider their options
3) A letter from a person and not an attorney is not generally that scary. A letter from an attorney's office carries with it more weight, and as a result, can intimidate a person more. It says "we mean business - don't even try it."
So if someone is threatening to modify the custody arrangement, a letter from counsel will be a good step in an attempt to curb their possible legal move.
If you want someone in WA, try www.marindale.com for a referral to an attorney near you. The attorneys are vetted and qualified and the service is free.
I hope this helps and clarifies. Please use the SEND or REPLY button to keep chatting, or please RATE when finished. You may always ask follow ups at no charge after rating. Kindly rate my answer as one of TOP THREE FACES/STARS and then SUBMIT, as this is how experts get credit for our time. Rating my answer the bottom two faces/stars (or failing to submit the rating) does not give me credit and reflects poorly on me, even if my answer is correct. I work very hard to formulate an informative and honest answer for you; please reciprocate my good faith with a positive rating.