I had gotten the Gold Symbols a while back but i remember it enough to give you some tips.
Firstly the Pyramid was one of the easiest places to beat, all you have to do is talk to the Psychic next to the PC before you go into the challenge. She'll tell you what kind of POkemon will be wild on that particular challenge.
For Example: your first ever challenge at the Pyramid she will tell you that she sees your Pokemon struggling with paralysis. this means that electric Pokemon will be wild (though i had seen a wild Vileplume
). The trainers on the other hand don't have to use electric, but then again they're all weak anyways. So here are my suggestions.
1st Challenge-Electric- Use electric resistant/absorbant Pokemon, if you have Swampert your set, Flygon would also do good here,you must also teach them earthquake, or the like, luckily they both learn it later in their last evolution, and lastly a Pokemon that has either strong defenses or can regain health (Latios/Latias, Starmie, Chansey, and the list goes on)
2nd Challenge-Poison-Use STEEL type Pokemon, they can't be hit by Poison types and can't be poisoned. Here i suggest you make use of Metagross (with strong Psychic moves), and Aggron (Double Edge etc.) and then of course a pokemon with strong defenses or can regain health.
3rd Challenge-Fire-These are harder to deal with but are still pretty easy, simply use a Flash Fire pokemon (i used Ninetales for reasons i'll explain later), then use a strong water type, Starmie would do good here, but Milotic would be better (if you don't have a Miltoic go with Starmie), and lastly, since you already have a Starmie on the team i suggest you bring something to wipe out the Frontier Brain, Aggron. The reason i used Aggron is simple. he isn't affected in the slightest bit by ANY of his attacks, BTW he uses Regirock, Regice, and Registeel.
Here are the moves i suggest for aggron-Earthquake, Flamethrower