I think you did a good job here overall Yisehaq! Keep in mind some of these rooms are big, the ambient light was not coming through the windows equally and you only used on camera portable flash.

Your metering logic is different from mine though. If the people are the subject then I'd meter the people...

Shot 1 looks fine but might have benefited from another 1/2 to 1 stop of exposure and we can see your reflection in the window. Using the white card on flash might have helped here (and upping the power if need be). Having the flash not reflect off the window should be a consideration in cases like these imo, just something to be aware of.

Shot 2 again might have benefited from another 1/2 to 1 stop of exposure. People at back right look quite dark.

Shot 3 looks decent but a full stop more exposure would have helped the background people. (Your flash handled the foreground person decently)

shot 4 look good to me and has the most perfect exposure of the lot. Shot 4 looks extremely natural and is my favorite way to shoot with flash as a general rule (so that you don't really see the flash too much)

Shot 5 looks good to me.

Hope that helps!
Marko