I have 18 adults to buy just in my family
That's insane. I can guarantee that a good proportion of those 18 are similarly stressed about the expense and effort of Christmas gifts as you are. The best thing you can do is agree on no gifts for adults, except perhaps partners and parents. They will thank you for it.
Look back at what you received at Christmas last year. Was the gift exchange worth it financially, as in did you receive good presents of a similar value to what you spent on others? I know you don't give to receive and it's the thought that counts, but most of the time, there is little thought, people are buying to fulfil a completely unnecessary obligation.
If you can't give nothing, just buy presents for DCs who are closely related and who you know well, and perhaps get the adults token gifts like wine/choc, but nowhere near 18 people, which really is madness.
But yes, plan ahead and save all year, but only after cutting down massively.