Port 80 inside the containers or outside them (on the Pi)? Having two listeners on the same host port will of course conflict, and wifi-connect will want network_mode: "host", which limits your port options in docker-compose (and there is no need to allocate port 80 to wifi-connect when it has host network access). However, wifi-connect does have an internal port setting that might let you free up port 80 on that end.
Alternatively, if grafana can run without host mode, then you could map a different external port to port 80 inside the container:
ports:
# outside:inside
- "3000:80"
The dashboard would then be available at [local address]:3000.