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These plants are normally ok a bit rootbound, so that is likely not the cause of your issues.

I would recommend checking the plants for pests, making sure the plant is getting enough light and water and that there are no diseases. The leaves can stay curled if the plant is stressed, but there are many things that can stress a plant. The ones I listed above are the most common stressors.

Spring is usually a good time for repotting/transplanting. The following article should be of some help to you: https://www.gardeningknowhow.com/houseplants/arrowhead-plant/arrowhead-plant-care-arrowhead-plant-or-syngonium-podophyllum.htm

I couldn't find anything significant about this plant family, though that doesn't necessarily mean it does not have value. Many of them, like arrowhead, have great air purifying qualities, which make them excellent houseplants.

Choose a vine or clump of leaves on the mother plant that appears to be healthy. Using sharp garden shears or scissors, snip it off at the base or wherever there are no leaves. Repeat this process until you are satisfied with the number of “starters” you have. Fill a container with water and submerge the vine into the water. Place this in a sunny window. Note: You can place several “starts” into one container. You may see roots begin to develop in 2 to 3 days, but it could take up to 2 weeks or more before roots develop. Once you notice roots, check it daily. When roots have developed to approximately 1 1/2 inches, they are ready to be placed into soil.

This article will help with its care: https://www.gardeningknowhow.com/houseplants/arrowhead-plant/arrowhead-plant-care-arrowhead-plant-or-syngonium-podophyllum.htm

You can make sure your rotating the plan to receive even light conditions.
It will grow longer stems that can be trained to grow up a small support or trellis, but you can keep it trimmed back if you prefer.

Here is a link with care information.
https://www.gardeningknowhow.com/houseplants/arrowhead-plant/arrowhead-plant-care-arrowhead-plant-or-syngonium-podophyllum.htm

The neem oil should be sprayed in low light conditions. This will burn most crops if they are in direct light. What you describe sounds like an iron deficiency. This is common in plants that prefer acidic soil. It is a sign that your pH may be starting to drift too high. I recommend adding iron sulfate to the top of the soil. This will break down with normal watering, and kill off anything in the soil as well as bring down your pH enough to put it back at the correct level.