I can't seem to deal with the demons and the neutrals for a long time. Maybe someone can suggest a tactic?

Well, you can do what Drakosha suggested: Take Deleb, catch a ballista, and run around with one dog, avoiding slow melee units while the ballista does its work; or you can catch a tent and then start summoning imps and try to... the main thing is to get Deleb's machines upgraded in the first three days, with a ballista or a tent. It's much easier to take out ranged units with the new demons, especially with the support of a tent.
Or you can take Grog with teleport to block ranged units if you don't have alt-demons.