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Most likely you will not get any fruit from this tree. If you want a better chance at fruit, purchase a dwarf tree that has been grafted onto rootstock at a nursery or garden center. That being said, it is not impossible.

If you are seeing lots of foliage growth with little to no blooming, then it's likely a nutrient imbalance - too much nitrogen, which produces lush growth, and too little phosphorus, which is responsible for flowering and fruiting. Without flowers, you won't get fruit. I would give the trees a high phosphorus fertilizer, or add bone meal to the soil. Here is more information: https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/phosphorus-plant-growth.htm

Oftentimes, lemons grown from seed may or may not produce fruit, but if it does produce fruit this may take many years, and when it does produce lemons, the lemons, MOST LIKELY, will not be edible or extremely slow growing. Since there's really no way of knowing for certain, you could try adding more phosphorus (bone meal) to the soil to help encourage the flowering and fruit growth.

I would try giving it some phosphorus rich fertilizer, like bone meal. If it is lacking phosphorus, it will not be able to produce blossoms (which means no fruit.)

The requirements for lemons are very similar to that of limes. If you have not read it yet, this article may also be helpful: https://www.gardeningknowhow.com/edible/fruits/lime/reasons-and-fixes-for-lime-tree-not-producing-blossoms-or-fruit.htm

I would separate them and grow as individual plants.

Yellowing leaves generally indicates a watering issue. Either to much or to little.
Make sure you have adequate drainage in the pots and are using a good quality potting soil.

Here is a link with growing and care information.

https://www.gardeningknowhow.com/edible/fruits/lemons/how-to-grow-a-lemon-tree.htm
https://www.gardeningknowhow.com/edible/fruits/lemons/propagating-lemon-seeds.htm

Here is an article on fertilizing lemon trees that will help you:

https://www.gardeningknowhow.com/edible/fruits/lemons/learn-about-fertilizer-for-a-lemon-tree.htm

Happy gardening!

These articles should help (the one for limes applies to lemons as well): https://www.gardeningknowhow.com/edible/fruits/citrus/citrus-fruit-thick-rind.htm
https://www.gardeningknowhow.com/edible/fruits/lime/dry-lime-fruit-what-causes-dry-limes.htm