Have you tried installing a WiFi signal monitoring app like: WiFi Signal. It might help you identify why you are having problems.
The built-in WiFi antennas are quite good in the newer MacBook Pro systems. Its located in the lid hinge cover. Review the IFIXIT guide for your exact system.
Yes, you might need to use an external WiFi adapter as the distance to the AP is too far. Here a directional antenna might be better if the external unit has a removable antenna. This is not the first thing I would do.
If you can move the AP to a more central location that should solve your signal issue and/or you may need to add-in a WiFi extender. As an example you could use an AirPort 1/2 way between where the signal is weak. This is the better solution.
Lastly, you could try a wired connection to see if the WiFi was the issue Vs the HughesNet. If you find the wired connection is just as slow the issue is more likely the WiFi router, or the HughesNet transceiver unit or satellite dish its self.
As to your HughesNet service. You might want to check your antenna alignment and check for something blocking the line of sight of the antenna to the satellite you are using. Even still the angle to the targeted satellite maybe on the low side (low horizon). You may want to check with Hughes on a better satellite (higher in the sky).