What is the best way to plant fruit trees?

If you look at commercial orchards, they are planted in straight lines. But that is for ease of spraying, pruning and harvesting on a mass scale. Most apple pollination is carried out by insects. So, you're really not overly dependent on wind as a pollination vector. The 15 - 18 ft distance is more of a minimum, so you don't have trees competing for resources (water and sunlight). If you're talking 5 trees, I'd let aesthetics rule the day.

I have three apple trees on my farm (left overs from when there was an 8 acre orchard). They are about 80ft apart and I have no problem with pollination. Apples trees can be high maintenance if you are concerned about production, lots of spraying and pruning. Also you may have to cull some fruit early to stop limbs from snapping under the load of fruit. Apple trees also don't hold up well in high winds once they get much over 15'-18' high with or without a fruit load. I keep mine about 12'-14'.

If you are from an area where apple production is a significant commercial crop, get to know your ag extension agent. I was able to triple production from my own trees after doing what my ag extension agent told me (from about 3+ bushels per tree to nearly 10). Plus, I get apples that are much more appealing cosmetically. Granny smiths make excellent hard cider, apple brandy, and apple butter.

Whatever works best for your yard, and you like the look of. I have mine planted in a couple of staggered rows. It's just what fit best, Pollination wise, you just want to make sure you have varieties that will cross pollinate each other. For instance, the Granny Smiths require one of the delicious varieties, Johnathan, etc. Not sure if yo u got semi dwarf or dwarf trees, a semi dwarf requires about 12-15' spacing while a dwarf will do fine with 8-10'. BTW that has nothing to do with pollination, just room for growth. If a pollinator is within 50' the bees etc will take care of the rest. The biggest thing to watch out for is look for the graft scar, and make sure you don't bury it. If bare root soak them for several hours before planting ...

Stark Brothers has a lot of good information regarding planting,pruning, and care. They are my go to for any fruit/berry questions I have. Their apple guide is worth reviewing before you get started, find it here: https://www.starkbros.com/growing-guide/how-to-grow/fruit-trees/apple-trees

I planted mine (5) in lines of 3 and 2, but staggered (so more like part of a bowling pin pattern). Also, 3 of them are multi-apple trees, with 4-5 different types of apples grafted together onto 1 tree (Fuji, Macintosh, Honeycrisp, Gala, and Braeburn). They can actually pollinate themselves. So, I have 3 multi-apples and 2 Granny Smiths. We also have 3 pear and 4 cherry trees, as well as 10 blueberry bushes.

Cpl Vic Burk Maj John Bell Washington State has a huge apple growing industry. Near Wenatchee, WA, as the apples reach maturity for all you can scarcely walk they the orchards for all of the poles supporting the branches heavily laden with apples.

Plant them where they will get sufficient sunshine and their roots won't entangle each other. If you are not going to commercially harvest, they don't need to be a straight line.