Can anyone help me with some ideas on how to improve my universe I am building?

This is about what I expected you meant in the original post. As long as you have internal consistency to your universe it's okay.

Nice! Opens up some interesting ideas like forcibly tattooing someone with a symbol.

Okay makes sense. Like I said before, as long as you have internal consistency and logic to world building it'll work out okay.

I'd be careful here. Just because the general society is hateful or racist doesn't necessitate that individuals are. I imagine it would be much easier to be racist against literally different races of beings, however. Like you said, it's hard and will likely take a lot of thought to fully develop.

Ah, I see. That's much better than what I thought you meant. Keep working on it!

I think this could be the single most important thing you need to work on. The alternate history and how major events unfold are definitely the crux of what makes your world. I'd spend a lot of time working on this.

And how did Alpha learn to make them? The scientists would have to have taught Alpha how to make them. Alternatively, they could have made at least one more and Alpha could have hidden and watched to learn the process. A final possibility, which, in my opinion, is kind of lame, is that Alpha has inherent knowledge of how to make them.

Keep developing this. Even with something like nuclear propulsion it would still take nearly 100 years to travel from there to Earth. Also, the dwarfs would definitely have a hard time when first coming to Earth. Everything from bone density to intraocular and blood pressure would be affected dramatically by lower gravity and atmospheric pressure. Hell, even the space travel would seriously affect the dwarfs in an extremely negative way unless you want the spaceships to have some kind of artificial gravity.

So they can live without oxygen? How about living with extremely acidic water? How about living on an even hotter planet because of the build up of greenhouse gases? Of course, this operates under the assumption that Nidavellir has similar atmospheric composition and vegetation to Earth. Which it essentially has to because the dwarfs can survive on both. Again, this needs a bit more work to make sense.

Great! Answering such questions is important for (you guessed it) internal consistency and logic. Cannot emphasise enough how important those two things are for world building.

Okay, stowaways makes sense. A 4½ year journey doesn't actually make sense. They would have to travel at nearly light speed. If the orcs possessed that kind of technology then it would only be reasonable that they had other superior technology like weapons. Given the time they arrive at Earth, the orcs could easily subjugate humanity. So why didn't they? Also, what impact did this technology (including the knowledge of how to make it) have on history? Having access to knowledge and technology beyond what we have today would be extremely significant in ~1250 BCE. Hell, even if the orcs didn't possess the technology to travel at near light speed they would still have super advanced tech that would greatly change everything on Earth.

I hope you understand my objective in asking these questions and making these observations. I'm not trying to say anything you've thought up is stupid or bad. I'm going to say it again: the goal is to have internal logic and consistency to your universe. If something exists, there must be a reason. The characters don't necessarily have to understand it but you do. Having a lot of details about your universe is important because it gives insight into how different stories might unfold. Small or specific details won't usually come up in the story itself but you knowing and understanding them will inform your writing.

Like I said, I think the most important thing for you to develop is the alternate history of Earth and how these different races and the existence of magic impact it. Keep it up!