To be a little bit more precise, the romance tile in the Keep represents who your Warden ended up with. In game it was possible to have multiple active romance fully complete, but that was due to bugs so it won't be represented in the Keep. They won't be doing partial romances because of before mentioned difficulty.
Now then if you romanced both Leliana and Morrigan, then basically use Witch Hunt to determine what your Warden's final choice was. If you step through the mirror you are choosing Morrigan and if you don't you are choosing Leliana. I believe I read they fixed it so you can have a human child with Morrigan even if you don't choose her romance tile, so that should cover all possibilities.