Negotiating work approval for a move (for fully remote / virtual employee) - any communication tips?

I am a fully remote employee living in the piedmont area of NC and working for a government employer based out of the pacific NW. The employer is wanting all of their remote employees to “shelter in place” and indicated that the only moves that are allowed are within one’s current zip code. We want to leave current area where we have been living for 10+ years, related to inadequate school system and a variety of personal factors I won’t go into.

I approached my work with a request to move outside of my current zip code and raised the possibility that I may have to leave and find a new job if I can’t move. After several months of deliberation they indicated they are willing for to move me to Vancouver, WA but I don’t want to go - too far from aging parents who are in central time and east coast.

I want to be able to communicate more effectively and am wondering if you all any tips for negotiation. All I have is:

“On further discussion We have aging parents with cancer and dementia in the Midwest and east coast and Vancouver is going to be too far for us to access them. Is there any way another location in central time could be considered?”

I realize we could just say and I can see them saying that, but just staying is not an option and I want to be able to effectively negotiate a third option. Any tips?