I've been just sort of keeping an eye on things without really commenting much, but I'll see what I can think of to help you out. Note that I have never tried these ideas myself, so take them with a grain of salt. A very large grain.
Pitfalls might not be a bad idea.
Just take your standard hallway, remove the lights and dig down until no one could survive the fall. Brutish, but it's cheap and makes people think twice about where they step. Pistons and plates can be used to supplement this strategy, shoving them off the edge of a cliff into death down below. If the trap is delayed, you might be able to activate the trap yourself, only for it to spring a few seconds later and shove down any pursuers.
If you have any TnT, I would make a small surface house that looks well designed from the outside with a wooden door and all that, but fill the area under the floorboards with TnT love.
Alternatively, you could just create landmines in general, although that might be hard. Just add pressure plates and TnT. Quick and dirty, but it get's things done. Put lava under TnT for maximum effect.
Lava in general may be your best companion. Assuming they don't have fire proof armor, I would create fire holes that you can dump lava out of onto invaders, burning them through their petty armor.
Another suggestion? Drowning them like rats. Make them think that they can enter a room, then find a way to lock it behind them. Fill the hole with water and watch them drown. Sand may have a similar, perhaps even more effective mannerism about it.
Final suggestion? Fear tactics. If you have books, write them. Write incredibly cryptic and horrifying statements into as many books as you can find and fill your chests with them. "Armok lusts for your blood." "All alone." "Slenderman awaits." Creep them the hell out. Put carts on eternal spin cycles and laugh as they attempt to figure out what the hell is going on.
Whatever you do however, make them pay for choosing to mess with the dwarves. They deserve nothing but pain for invading the mountain home. Do not show fear. Do not show mercy. FOR THE DWARFDOM!