Isolated Multiplayer Connection Issue

When I try to load into my sisters world and vis-versa, we can't connect online. It will show connecting to server and then show and unable to connect message. The problem is, it's only happening between my sister and I's Switches. We were able to connect to her friends world without any problems.
We've troubleshooted in every way we know and what has been suggested. We've contacted our internet provider, checked our NAT types, reset and hard reset our Switches. Archived the game and redownloaded it, and contacted Nintendo and Mojang customer service. We are able to play other multiplayer games together like Splatoon 2, but not Minecraft. We noticed the problem after the version 1.7.0 update.

Please help. This has become extremely frustrating. 

We play on the Bedrock Edition for Nintendo Switch. 

Thanks!

-Chanel