The R Pi only has one serial port, so you can't do it that way.
You can sort-of do it with an Arduino. You have to use hardware serial for one GPS and software serial for the other.
The GPS will only use one antenna. If you attach an external antenna, that's the one it will use.
An Arduino should be able to handle two NMEA streams at least up to 5Hz. That's equivalent to a single stream at 10Hz, which a Uno can handle.
You might want to consider a 32U4-based Arduino, since the hardware serial port on those is not used for uploading and serial monitor. If you use a Uno or Mega, you would have to disconnect the GPS every time you wanted to upload a sketch.
You could also use an M0-based Arduino. The M0 does not support software serial, but you can define additional hardware serial ports (Serial1 is already defined for you)https://learn.adafruit.com/using-atsamd ... new-serial