I guess you know everyone's opinions by now. Please get Monster neutered before he starts learning undesirable male traits. As for as the mom of the King Charles Cavalier, she should have her spayed. Unless she is determined to try to breed her and risk her life the sake of getting more "cute puppies" she should know that the more her dog goes into the heat the better the chance she has of contracting Pyometra.
http://www.thepetcenter.com/sur/pyo.html
We lost our 5 year old yorkie Cecily due to our ignorance back in 1979 and I wouldn't want to wish that experience on anyone.