Overlapping the elements (either warp or weft) takes a little patience, and over time with practice, your joining will look seamless.
Inserting a Warp
While Twinning a small hat, this video demonstrates a way to add in a warp.
Inserting/Extending a Weft
As you are twinning, you may need to insert a weft here or there. In this video I demonstrate how to insert a short weft or a long weft.