We can all add to the dream, our personal views on what we like and want out of a glamping holiday - but we can't answer your AIBU without your business plan.
Have your family members who think it is a great idea done the detailed business plan? Looked into all the legalities and liabilities?
Is there planning permission for a glamping site or would you need change of use? Is there already mains water and electricity? Getting connected is costly and takes time. Is there a septic tank / mains sewerage or would you be looking at soakaway and compost (the eco site model? I am guessing not if you intend hot tubs)
Capital costs of drainage if the land is wet, pitch levelling, building platforms, all the facilities . Overheads: Public liability insurance, buildings insurance, business rates, council GIRAMS or 'mitigation' payments, commercial waste licence, water bills and costs of tunning hot tubs, cleaning and maintenance costs - toilet unblocking, showers and toilets cleaned twice a day. Legionnaires monitoring and checks, etc. interest on loans.
Have they done an audit of all the sites in your vicinity and monitored Pitch Up etc to see how full / empty they are at different times of year? And what the charges are. Booking fees costs.
Have they looked at all the websites on 'how to set up a campsite' - including the government page on licensing?
Start with the business plan!
I camp a lot, tent camping, but smallish niche sites. All the owners I have chatted to do it as a sideline /diversification to their main income. Would this be your main income?
The ones that are run as a permanent sustainable full time business are much bigger
I am all in favour of camping and glamping sites, so good luck!