Is it the fptr or the order in which the stitches are worked that is the primary problem?
Front Post Treble Crochet Technique
Double Crochet cross stitch
shows working the stitches to cross them. This video doesn't use fptr but you can get the idea of how a stitch or stitches are skipped and then worked out of normal order.
Cross Cable 2 Crochet Pattern
This video isn't exactly the same but you can see how he works the stitches out of order. Check the other videos on the page too. If this doesn't help, let us know and someone should be able to come up with something helpful.
That's a beautiful pattern, worth the effort of learning the technique.