I currently have a single 5ft long vanity and would like to know if it is possible to install a double sink vanity top to it. I would like to keep the cabinet portion but would like to add two sinks to the top. If so what do I need?

First get inside and under the sink to make sure the space you need is actually there, sometimes you will find bracing and/or drawer tracks. If the space is open you can try to find a stock double that fits a 5' cabinet or order a custom sonk from a home center, cheaper than you might guess.