Within the caveat of personal taste etc etc, my limited take FWIW is that the Castelnau is a lot of fizz for the money, especially if you can manage to grab it when on offer - sometimes working out as low as £20/bottle. I’m not a huge fizz person though, and can’t comment on the others.
That white is really good for £8 and should work with ottelenghi-ish dishes. Depending on your budget, the Marty McFly Furmint is in my view really really good for the price, really tasty and with a just a hint of a wee spritz to it, and it’s hard to imagine it not going down a storm with anyone really. It can take a bit of spice too.
And the Xinomavro is really good too, especially if lightly chilled, and should also work nicely with the food.
Whatever the wines come to be, enjoy the wedding and the tastings beforehand :~}
For Crémant vs Blanquette, in the context of miscellaneous wedding guests I would stick with the former. I know that for some palates, Blanquette’s dominant mauzac will bring quite a sharp apple flavour not always appreciated.
You mentioned no red meat. For reds I’d have a look at some Beaujolais and lighter Garnachas. There is a Cebreros at £9.99 on WS that might be pretty good with tomato, vegetables, etc. Might be worth setting a tasting of four / five bottles with friends.
Unusual varieties are not so much the problem, but unusual flavours might be. Also, many people may prefer cheaper wines that they are more familiar with. With all that in mind, I’d seriously consider Prosecco as an option for the fizz, or a cheap Champagne if people are likely to see the label, as that will be appreciated just for the name. For a decent quality cheap red, grab a bottle of Toro Loco next time you are close to an Aldi, and try it. I hope all this does sound cynical - it’s not meant to be.
But to answer with my wine geek hat on…
I think the Jeunes Vignes would work well with the food, and may even be a crowd-pleaser, though I have not tested it with non-wine-geeks.
I would also be tempted to serve one of my favourite cheap reds, which I think works well with middle-eastern food: Ksara Le Prieuré. It can be had for £11.50 or so.
For fizz, I like The Society’s Saumur Brut, but it does have a rather distinctive Chenin taste. Get The Society’s Champagne if you can stretch to that.
For white I think the Aldi Assyrtiko would be a good choice - for £8 (Edit: actually £6.99). It might be a bit too austere for some.
Orange wines would also work with the food, but I wouldn’t dare serve one at a wedding.
As for reds, I don’t know about your budget, but yo can save some money by going for the ridiculously well priced Jaume CdR 5 litre bag-in-box. Super wine, maybe not great on a hot summer day, but fruity and friendly.
I would echo others views that many cremants are as good as the cheaper champagnes and better value . I cant say I feel the same way about prosecco which mostly has a very distinct (and far less attractive) floral taste IMO.
My go to Cremant is the Cave de Lugny from Waitrose, normally £14.99 but look out for the regular 25% off deals.
The Furmint might well be a bit “marmite” and a safer bet would be a sauvignon. The wine soc Villargeau coteaux du Giennnois is a reasonably priced crowd pleaser.