do you have pictures. since they are already stained they will need to be refinished. stains that have quality pigments will fair better. the finish will you the protection. depending on exposure will determine the finish.

Here’s the worst of them. The sun beats on this door from 2p-sunset. The French doors are under deep porches but the stain is still flaking away on them as well. The doors look so dehydrated and they’re only a year old from being installed. The back story - we were supposed to get fiberglass but the supplier messed up and got wooden doors. They said don’t worry about it and we scored the Fir doors for the cost of fiberglass. When the painters asked what to stain them with, I was too quick and told them to stain them the same as the baseboards which are Varathane early American. I want to stain them a rich ebony color since my windows are black. Right now the stain clashes with my baseboards b/c I was an idiot, not thinking about fir being pinkish and my pine baseboards being yellow so the stain obviously takes on a different tone. I was mentally done with making decisions that day and spoke too soon.

I would use a Dalys ebony stain and finish them with a spar varnish or marine varnish. they will need to be stripped, sealed with benite ans stained. if you want them closer to black you'll need to dye them first then stain. after they are stained do 3 to 4 coats of varnish sealing all edges tops and bottom as well. this will give you the best shot. you can also look into 2k polys they are extremely durable as well.

It’s sounding like a job I would rather pay someone to do lol

i would hire someone it can be tricky and time consuming. and when done correctly the doors will look great. they will still be on a maintenance cycle.