That indeed fixed the whiterun problem, by grouping them together.
Great, now to find the reason for your Elin staying at adult scale. Are you using the non-nude or nude Tera body? The plugin for the nude body should have no affect on scaling, but I'll give it a look anyway.
Out of curiosity, if you have the Enhanced 3rd-Person Camera mod, reset the camera then uninstall it. If it's removal has no affect, you can reinstall it.
Enhanced 3rd-Person Camera. Optional, but keeps the camera view from being too high for small characters.
Enhanced 3rd Person Camera-29990-v0-9.rar 104.57KB
Did you install the Unofficial Skyrim Patch? By having the "USKP Patch for Race Compatibility.esp" you need the Unofficial Skyrim Patch to prevent the game from crashing.
The Elin NPC and Enemy mod replaces some NPC that came with the game. It also adds new Elins. If you speak to an Elin and she says "Hello!", or "Can I help you?" and nothing else, those are the new Elins added to the game.
If you speak to them and they give a dialogue or you get a dialogue menu, those are the vanilla game NPCs.
The Elin NPC and Enemy mod does not change dialogue.
To recruit Rin the BnS Lyn follower, speak to her and a dialogue menu appears. Choose the option to ask her to follow you.
The Elin NPC followers, such as Housecarls and Aela, can be made followers in the same manner as the vanilla characters. Speak to them, receive dialogue menu, and choose to have them as a follower.
The 3 Elin mages at College of Winterhold can be made as followers the same way. Just speak with them and get the menu options.