How many vent lines do I need in a bathrrom if I have a tub shower and sink. All three will tie in o a 3in line that dumps in to a sewage pump. Can I just vent the main line?and can I tie into a vent line that is being used for the plumbing that is used for some other stuff?

You will only need one if wet vents are allowed in your area and your rough goes down like this.
Toilet connects to sewer main or the stack vent. Lavatory connects to toilet drain and runs a vent off the top the stubout tee out the roof or revents back into a dry vent in the attic.. The toilet wet vents through the lavatory vent and the tub/shower connects to the lavatory drain and is wet vented by it. This is a normal rough in and is acceptable both by local and state codes and also The Standard Plumbing Code Book in 90 percent of the country. Check your local codes.to make sure you're not in the excluded 10 percent.. The vent off the lavatory may be run out the roof or revented back into a dry vent in the attic or if you're reventing back into a fixtures dry vent you must make your connection at least 6 inches over that fixtures flood rim.
Good luck, Tom