Definitely check the laws, but if the mother is living there and is not on the lease you may have legal grounds to evict them. I would avoid that if you can but definitely ask them in a polite way to leave. I would say something along the lines of "I understand that this home may not be a fit for you, so rather than you staying and fulfilling the lease and being unhappy, I'm happy to terminate the lease early so you can find another home that is a better fit for you."
Additionally, look into your local squatter laws. In some places, if mom is there too long, she then gains legal tenancy...
Long story short if they are unhappy, not only with they be difficult to deal with and live near, but they probably won't take care of your property as well as you would like. Plus, when they do bring legitimate concerns, you may not respond as quickly or take it as seriously because there have been so many illegitimate concerns.
I would give them an out to relocate and re-rent it out to someone else who will enjoy the place more and be less challenging to manage.
Good luck. Don't be afraid to have it vacant for a month or two if need be. It will save you more money in the end (coming from someone who learned this the hard way). :)