If the GFCI is in the same three gang box as the switch for the fan
and lights you should be able to reconfigure the wiring to eliminate
the light and fan from the GFCI protection.

No, the GFCI is in a different box on a different wall. Power comes from
the GFCI over to the 3-gang box, then three cables exit the switch box to
go to the fixtures (ceiling lights, vanity lights, bath fan).

There wouldn't be an easy way to take the fan off the GFCI.

I wired both bathrooms in our own house the same way, with the fan on the
GFCI, and we've never had a GFCI trip. So it has been odd that my in-laws
GFCI trips so often with the same wiring scheme.

Anthony