If it were mine ....
I would joint the edges or rip them on a straight line jig.
To prevent gaps, the edges must be square and straight. For a rustic look where gaps don't matter that much, then barring any severe curves, I would just glue them as is.
The use of Liquid Nails in the splines isn't a bad idea, since it will fill the gaps as well as hold the planks together really well. Some cupping is evident in the photos, so depending on the "look" they may need to be surfaced on the jointer. If the surface looks good as is, then that would be unnecessary.
If possible turn the cups alternately which will help keep the whole unit from warping. Some advise against that, but it won't hurt.
The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
Last edited by woodnthings; 11-02-2015 at 08:32 PM.