Thanks for all the suggestions.
I thought about a flesh coloured backing, or wearing a flesh coloured slip but I don't even want it to look like I have sheer bits in potentially inappropriate places, especially for a Muslim wedding
so I'll just make sure they are only revealing bits of skin I don't mind having on display!
The bride is not superstitious at all and I'm fairly sure there aren't any peacock feather issues in Muslim culture - peacocks are a symbol of royalty so they'll just think I have ideas above my station!
I got my fabric out and I think the silk dupion is more like a raw silk - I'm not sure what the difference is to be honest, but this is finer and more slub-y than silk dupion I've used in the past. It's also fairly transluscent so I am underlining with subtle grey wax printed/ tie dyed cotton (instead of the silk organza I originally planned) which gives a lovely effect when the light shines through it.
I've cut out all my pieces and marked all my stitching lines on the underlining and now I'm just hand-tacking my layers together, then I'll get to work on the sheer back panel (pictures soon!).
I'll do a hand tacked fabric fit before I sew everything together properly.
I probably won't even be able to dry clean this dress with the feathers, etc., so I'm thinking I will make a separate slip instead of a lining, with thread chains and snaps to attach it at the shoulders, as well as removable dress shields at the underarms, so at least those bits can be washed!