Playing orc means having less map control. You should do everything to change this as soon as you can. Easiest way to do so is upgrading your troops or increasing their size. Neither you make every player do this - what would lead to a very fast result - or you keep at least 2 players upgrading troops for the rest of the game. This should be done by mages, like Lady Jaina or Fung, heros that don't need items immediately to be strong. Level 3 troops will already dominate human troops in a way, that they have still enough ressources left to heavily weaken human towers.
If you gather to start a push - and that is something you should do regulary - hire catapults. Towers will snap like straw under their flak.
But what ever you do, protect your Lords. Make sure that you are always able to teleport with enough health and mana, to be able to defend those units. Losing a lord means losings for every allied unit on the map and a bunch of gold for human players.
If pushing the castle directly seems too hard, try to kill human workers. Focus those spots you suspect to be the ones of players upgrading troops too. Human troops are stronger than orc troops with same level in general.