Given Fiji airways has officially entered OW, and they still cannot be used for a OWA, suggests there might be a bit of a lag between the airline joining and when you’ll be able to secure their seats for the purposes of points capping.
Oman Air, Fiji, Jetstar and emirates (plus others) are all points partners. You can select them as part of your multi-city award, but they won’t cap the points. They’re not eligible for OWA (either outright or ‘not at the moment’)
It’s a good question as to whether someone like Fiji or Oman would reprice at a later point. We haven’t really had any example of late to draw on.
Rather than Oman via MCT you could potentially look at Royal Jordanian.
constructing your itinerary without a points cap means the flights you have pencilled in would already come to 624k per person.