Our house has sewage smells coming up from the sink and toilet, especially after using the shower or toilet. It also smells in the kitchen as well.We live in an old farm house(handed down) and are not sure if there is an air vent.

Of course 100 years ago, there was most likely not even indoor plumbing, all that would have had to be added.

Is there a vent ( or several ) vent pipes coming out of the roof of the house, or at times out though the side and up to the roof line

Chuck nailed it! Simply look up to your roof. As a young boy back in Wisconsin we had older late 19 centenary homes. They were plumbed with a single 4" line running from the street through the house and out the roof. Every fixture in the house connected directly to the 4
through a "S" trap. That's how I remember how older homes were vented. Regards, Tom