Since we do not need their part of the 7.5 to access our property, do we have grounds for termination, since they are obstructing the easement and won't let us use their part.
No, that does not create gounds for termnination.

Unless the esement specifically allows parkig on the easement (possible but very unlikely) there is no parking or other obstruction or any other use allowed.

So how to go about resolving the problem?

Best to get a local attorney for advice and to to write a letter to the neighbor, pointing out that parking on the easement is a trespass, and a remedy might end up as towing. Not trying to write the attorney's letter for you, but that is my best advice based upon my own experience. Don't try to save money and write a letter yourself.....

Good Luck!