What I’m doing is making a story in the medieval times and I wanted to make up a village and have my characters be there and travel around there but do I have to make everything around there in the book like how it was in real life? For example if my character where to travel south, in real life he would reach Berwick castle but in the book I don’t want anything to be there. It’s important to me that it’s set in the real world because the second book is supposed to be in Wisconsin so I don’t want to switch from not real to real. (Sorry if I’m confusing)
Jane Austen routinely did what it sounds like you want to do: she kept the big places intact (London, Bath), but the estates mentioned in her stories (e.g. Pemberly) are fictional, with only their general location given. The estate was fictional, but culturally it was set in its time, in England, which is all that she needed. Similarly, you can invent a village, and not bother too much with precise distances and where exactly it should be on the map. Pemberly could have existed, so could your village. In fact, I believe this was a common way of writing at the time.
The location serves the story, not the other way around.
If you need to alter geography a little bit, that's fine. It's called artistic license, and everyone does it.
The danger is that changing the real world risks throwing readers out of the story if they are familiar enough with the area to recognize the changes. They'll get distracted by the details, and you don't want that.
You can reduce this problem by obfuscating the details. It's fine if you know the exact spatial coordinates of your town. But if all the readers know is that the town is "somewhere in Europe by a river" then they won't know that there should be a castle there.
I think that at this point you must consider the importance of the location to the plot or the message you want your readers to get. For example, Dostoevsky, in Crime and Punishment, omits street names by just giving their first letters (interesting reddit discussion in here). While some speculate he did it for censorship reasons, I viewed it at the time as a tool enforcing the reader to be more focused on the story. Hence, by omitting real locations, the reader will not be attempted to memorize street names because they are not crucial to the story. From fear that some people may debate me on this with regard to "Crime and Punishment", I will just conclude with the following:
I do not see real locations as important in stories. As long as the setting is consistent (i.e. you do not jump from place to place uselessly), I think you should be fine. When you say
It’s important to me that it’s set in the real world because the second book is supposed to be in Wisconsin so I don’t want to switch from not real to real.
I think the best advice is just to not care about locations and focus more on character development in this part of the plot.
Another example of not real to real stories is in the Agota Kristof's trilogy: "The trilogy of the twins" (The notebook trilogy). If I remember correctly, the first book does not give you any indication about what the real location or time are. Next, it becomes more clear and uses more "real" descriptions. This comes up as the location and time become more crucial to the story-telling.
I think that would be fine to do! If you take Cassandra Clare's The Mortal Instruments, for example, most of the series is set within New York. However, she made up the country of Idris for the home country of her made up race of Shadowhunters.
It's your story, you can set it in any type of world you would like!
A quick google search for Bernice castle came up with a bunch of females with last name of Castle. Searching for Bernice Stronghold also came up blank. So if google can't find that castle with all its modern powers, it is forgivable that your characters might miss it as well.
Just leave the exact name and location of your village obscure. Give your readers nothing to search on, and they will not be tempted to search for discrepancies like a missing castle.
So instead of referring to the village by it's name, call it "our village" or "our home". Refer to the next town over as "that small hamlet where cousin Mary lives". You can even have your character's give the neighboring town a disparaging nick-name and use that in place of its real name.
Also, humor can also be used to justify missing details. If the narrator sarcastically points out the idea that nobody ever mentions the name of this particular town, then everyone's efforts to avoid disclosing it can become a great point of humor. Think obscurity through absurdity.
Do as much research into the place you want your fictional village to be as you can. Find out the topography, the climate, the surrounding large towns. Know something about the people of that time and region. At the very least it will grease your creative wheels and give you the ability to flesh out your fictional town with some degree of authenticity.
If you want to deviate from what is really there, for example you want Berwick Castle not to exist, then just make up a reason for it not to exist. Who built it? That guy just happened to die in childbirth. Easy enough. The main thing is just to make sure you know what is in your world in RL, and when you deviate, do so by choice, not by ignorance or apathy.
Depending on how much you want to deviate, there may be a lot of work involved. For example, if you want a huge stretch of wilderness for your story, in a location that in RL is quite thickly inhabited, you need a good reason for that. Maybe a plague? But if so, how did your town survive? A war? Then there would be ruins. A hostile force of some sort? Then the story needs to deal with that hostile presence.
Of course, you can choose to ignore all this and just arrange things however you like, and many readers wouldn't notice at all. But if you are writing a story that includes alternate historical elements, your target audience is likely to be knowledgeable in that area, and is much more likely to notice any mistakes.