On VH you are probably just screwed. I've faced the same basic scenario before. It isn't winnable in a single battle. With current stats archers and javs are wasted if targeting them--8 units of archer auxilia could not get any kills as they approached in a medium test (and the chances of killing anyone in the archer towers is negligible.) Javelins don't kill them. Javs should be used for melee against them (that is where the +6 bonus applies.) However, you can't succeed with that and deal with the rest of the army and other elephants as well. The javs will rout because of the other units hitting them. Flaming arrows might help to shake their morale...I don't use them because of some issues with them.

What I have done now is simple...I modded elephant stats. Right now I have the armoured elephants at 6 hit points (vs. 12 in the patch, and 15 in the original unpatched version of the game) and I reduced their armour down to 9 with a boost to their defensive skill as compensation. I had to boost their strength vs. cav--because high charge bonuses of some cav and camels was allowing these units to kill elephants. The new combo will make them somewhat vulnerable to missile fire and yet more likely to die in melee.

If you hold back some cav, you might be able to hit individual elephant units and get them to rout. It is a bit tough with the 12 hit point units. Yes, this is completely non-historical use, but CA's stats don't do much to emphasize proper use. They get swamped by charge tactics. Cav armies are far more effective than infantry.

Focus on beating the rest of the army first. Elephants will almost all heal after battle, so focusing on killing elephants won't work, unless you win the battle outright.