The smaller one out of the same seed is a hybrid the larger one is true to the fruit. You could separate then no. But i Usually wait until they are two Months old before I separate them .
Trace

Thanks! So they'll do alright in the tiny pots for awhile? It will be interesting to see what the hybrid is. They came out of a Rio Star grapefruit.

You can leave those seedlings in that pot till the tree is 6-10 inches tall. When it gets warmer you will need a larger pot. Clay pot loose moisture through their side and cool the root to much. You can put the pot in a black plastic pot to hold moisture in and collect heat while our homes are cooler than the citrus trees like.

Does the name Oregon after your forum name states that the tree can never be planted out side in ground. If you are looking for something of beauty you made a top choice. If you are hoping for fruit You will probably need at least a 30 gallon or larger container to do so. You will need to follow the strictest pruning methods for maximum viable root volume for your container size. You will have to pick a citrus mix suited for your area. You will also need to step the container in gradual jumps. I planted seeds from tangerine that was marketed as a "Sweetlee" and they are now just over 2 years old from sprout. I planted them outside permanently in ground. I use a lean-to greenhouse to protect them in the winter and the GH comes down in spring till fall. My trees are in a pit about 8 feet deep and can grow another 7 feet for a height of 15 feet max. This might be an option for you.

If you can plant outside as I did you can up size the containers much faster

Grapefruit tree gow faster than tangerine trees. Here is my sweetlee at 3 months from sprout.

Best of luck to you and your seedlings and water with warm water frum underneath so the stem stays dry and free of damp-off, Damp-off is almost always fatal

Steve

Yes as Steve said u can leave them in smaller pots until warmer weather. Clay pot do lose moister quicker that's good and bad. You don't have to worry about damp off as much but keep a closer eye on water. I wooden dowel works good until you get a sixth since of watering. The top inch of the soil should dry out before u water again.
Trace

So the shirt seedling outstripped the tall one and stuck a root out of its clay pot. Hopefully this picture of the current situation will post.

When I replanted my trees I placed it so a 1/2 of root was above the soil. This cured my damp=off problem. I see you have done the same. your on the right track.