@J.H.Z From what I can understand, you are using a physical keyboard connected to an Android device. It is general helpful to indicate which device is being used, its Android OS version, what type of keyboard is being used and the version of Parallels client in use.
As
@Eugene. K. mentioned, it is advisable to use the PC keyboard layout when using a physical keyboard. In your case, it seems that this does not work correctly.
As a self-fix first step, I would suggest to confirm that you check that the RDSH has the correct keyboard layout (US International) when connected. Secondly, try to use AltGr or Ctrl+Alt (keys for this layout:
https://web.cortland.edu/ponterior/keyboard/).
If you are using the US International keyboard layout, you should be able to use the "dead keys" functionality (where you type " ' " followed by " a " to get " á "). The "dead keys" functionality might break backspace sometimes, since "dead keys", once pressed, can not be cancelled with a backspace (need to press "space").
If the above does not help, you could also try to report the issue directly to the official Parallels support and provide the OS/device/etc information.