Birds rarely come into a house except by accident, they are more likely to nest or roost on the roof. Birds will enter the attic if the screens are not in place or have been damaged (quite likely be another bird), and through damaged soffits or fascia.
Since birds leave their nests regularly it is relatively easy to remove them. Bird droppings and nest material needs to be removed from any attic space, care should be exercised – the droppings can cause a serious lung infection – histoplasmosis.
Small birds, like starlings, house finches, and sparrows, prefer gutters, chimneys, and eave brackets. Removing the nest and sealing up the cavity or filling it with wire mesh will usually discourage them. Bigger birds, like crows and pigeons, are not going to be shooed away or discouraged by nest removal or plastic owls. Use of products like Nixalite (porcupine wires) and Bird-Proof Gel that make roosting on horizontal surfaces impossible.
Wood peckers can not be harmed – endangered species. You may be able to get a permit from the Department of Wildlife allowing you to remove the woodpeckers.