Recommendation for Apple Trees

Hello, I'm very new to gardening and even newer to permaculture and I'm looking to learn what I can do to enhance my growing experience.

I'm in the piedmont of NC (7b/8a) and I've got a honeycrisp apple tree and a granny smith that I planted about two years ago about 10-15 feet apart from each other. I would say they are about 5-6 feet tall now but still quite thin and immature. At the time I planted them, I figured for pollination the two varieties would be enough but I've since realized they could use some support from helper plants and that's part of what I'm trying to figure out now.

The soil its planted in is classic NC soil, pretty dense and clayey. Originally I had maybe a foot radius clearing around the tree and used black mulch because we had some laying around until I realized that was a no no. Switched to aromatic cedar mulch and cleared more space around the tree and will likely have to clear more, as the grass is fighting back.

During the warmer months, I water the soil and I spray the trees with a homemade neem oil mix and cedar oil mix every week or two to keep pests away, mainly japanese beetles which have absolutely destroyed the trees' foliage in the first year. This with a mix of hand harvesting the beetles reduced the damage to the trees significantly for the second year but it's still a problem. I've heard marigolds are good to keep them away but pretty much open to trying anything.

I feel I've been a bit lazy with my care of the trees (especially since they are planted at a relatives' 30 mins away), so my goal now is to have a plan before it gets warm again to make these trees sustainable and pest resistant. I plan to travel in the future and be away for larger periods of time so I want these trees to hold up because I know my relative isn't gonna do jack lol. Thank you!