I think op got the response they did because of the tone of their posts - the op started 'OMG' for starters. Then there was the drip feeding/possible factors for agreeing with op.
Seems to me though that the op is the one making assumptions
assuming they'd be able to invite guests to someone else's wedding
assuming they'll be expected to contribute (and a hefty amount too - my big white wedding cost £2k all in! 150 guests too mind 20 yrs ago) it's 2 years away it's entirely possible the b&g are planning to save/pay up for the wedding.
assuming this was the future dil's decision (surely at least a joint decision between b&g possibly given the groom is the one that knows these friends he's the one that DOESN'T Want them there)
Despite a large wedding I had none of my parents friends there (my side of the family - Catholic - huge so even that needed trimmed!) but my groom did (BUT he'd lived with his mums friend at one point when his mum was seriously ill so she was effectively his foster mum, the 2 sons are best friends and her son was his best man. also his father was a long term foster child and it was his foster grandparents that were there not his blood ones).
Every wedding is slightly different.
If you are ASKED for a large financial contribution, there might be scope for negotiation. But if you OFFER it should be with no strings.