On spaying: cavaliers have one of the highest breed rates of pyometra, an extremely serious womb infection which often is fatal and at best, requires emergency spay under very risky (and costly!) circumstances. According to an insurance study cavaliers were one of the highest risk breeds with females running close to a 40% lifetime chance of pyometra. Unspayed, they also have a 25% lifetime risk of mammary tumours -- an aggressive cancer with a high rate of malignancy in the uomours.
Pyometra is horrific and extremely painful for the dog and typically an owner will not notice anything is wrong until it is a serious emergency. We have had several people here lose cavaliers over the years to pyometra. Rescues regularly see older dogs come in with mammary tumours.
Once a dog has had a false pregnancy they often continue to have them and they too can be a cause for an emergency spay -- I have had to do this with two rescues stuck in a cycle of false pregnancies.
There is simply no way that a spay is riskier than NOT spaying a female cavalier -- that's setting aside any other concerns. I've spayed hundreds of dogs in rescue, and have never had an issue. If you have a male puppy, you will have to neuter one or the other or both or you will have a lot of separate management on your hands for about 12 weeks out of every year when they can have no contact and may well shred whatever space they are kept apart in trying to reach each other. Nature is pretty powerful in driving intact dogs to want to be together and a male can scent a female in heat from over a mile away.
And yes --this could be a cause of your indoor accidents. I have had marking females (still have one, spayed, and housetrained so she doesn't do it indoors).