I've done half of Ben Nevis, when it snowed in August

and Scafell Pike about 20 years ago.
However, there's a team of us doing it including others who have done the route plus support vehicles. That should be OK, hopefully.
As already said I wish you all the best and if you are a fit guy who can move quickly over rough terrain you may well be ok.
It is a hideous challenge though and one that I would not enjoy at all - but such is the nature of these events.
I admire anyone that completes this in sub 24 hours - with well over a thousand (I keep records sadly) mountain days under my belt this is not something I would contemplate doing.
BN is a decent enough hike for one day and is a fair bit of effort even up the Tourist Route. SP is not too far behind and whilst Snowie needs little effort in the right conditions stringing the 3 together is my idea of purgatory. But then I'm a wuss!
I'm not sure how anyone does it tbh as the travelling time is a whopping chunk out of the 24 hour allotment.
I think the target times are BN 5 hours, SP 4-5 hours depending on start point and SN 4 hours from the foot of the mountain as opposed to a fair way up at PYP I presume? That's for hill-fit, hill-savvy people. 14 hours is a long mountain day without the travelling involved.
Hope you raise loads-a-money!