Question about removing some walls

We live in a house built in 1890. Our kitchen is small and badly set up. There was a large set of windows on one wall, which kept us from adding cupboards, as the windows started low, just like the rest of the windows in the house. Another annoyance for me is that there is a bathroom that you enter right from the kitchen. Bad placement. Next to the bathroom, and also entered through the kitchen, is a small entryway.
Recently, while painting some trim, I noticed something. The exterior walls of the kitchen, bathroom, and entry all had identical wood trim, which matched the trim in the rest of the original house. The door between the bath and kitchen, and the door between the entry and kitchen, had plain trim that didn't match anything else. Also, I noticed that the walls dividing these rooms are not plaster. They are some sort of cheap board that has, more or less, some kind of tape joining it in places. It's all been painted over, and we didn't really notice it before now.
So I am now thinking that the bathroom and entry walls were added later, and that the original kitchen encompassed all three rooms. Those large windows would make much more sense if there was more room in the kitchen originally. They might have set a kitchen table by those windows.
I would love to go back to this layout. I'm guessing that, if those walls are not original, then they must not be load-bearing? The only thing that concerns me there is that there is a bathroom above the one that I want to remove, and it has a cast iron tub in it. Is it possible that the newer wall was intended to bear some of the weight of the tub?
I guess I am in "dream-mode", thinking about what a great kitchen I could have if we tear out those walls (the bathroom could be relocated), but I don't want to get my hopes up if it's a bad idea. I really don't know anything at all about structure. You couldn't tell, could you?
Anyway, any thoughts from the experts?

You may need someone to come in and look around. The original bearing walls would have been supported from below as in foundation wall or beam below the floor. If the plumbing was added some time after construction, this wall may be hiding the plumbing for the bathroom upstairs and may well be helping to spread some of the load.

A few of the first checks are relatively simple for anyone to do...usually.

Find the floor joist direction, bearing walls are perpendicular to them both top and bottom.....usually.

Bearing walls on older homes like yours are usually stacked on one another...or close.

As Neal said, bearing walls are usually loaded all the way down to the foundation, by way of beams, piers, or other walls.

Take a look around, then call someone to verify what you think you are seeing. Houses of that time period are notorious for having floors that are over spanned by today's standards...the wall could have been added to help that.

Okay. Who do I call? Contractor? Architect? Structural engineer?
Thank you for your help!

I would call the engineer, he can tell you what needs to be done.

Definitely an engineer...he will do actual calcs on it...some contractors will use their intuition instead of data...not always good.