This is absolutely meant to be informational, not preachy, so please read as such ... it's not meant to put you off either, although it might sound like it LOL.
Welcome to the potential world of dog ownership. Choose right, and it's great! Take your time to decide on the right dog for you all, but please also take time to find the right puppy to buy that is raised with love and care, well socialised and will give you the best chance of an easy and loving family member for your first dog. Make no mistake, it's a bit of a minefield these days, unfortunately, and getting much harder to see through clever sales scams. 
You have chosen two breeds and one crossbreed that are absolute puppy farmer gold. Am not saying that they are bad choices in themselves, but PLEASE read up on the evil trade of puppy farming and do your very best not to put money in these people's pockets.
As well as the fact that you would be supporting a life of misery for the dogs involved, you could well be buying yourselves a whole heap of heartbreak and expense. Poorly-bred Westies are very prone to skin issues. Poorly-bred Cavaliers are prone to endless horrible issues. Crossbreeds do not magically negate any health issues, but rather are more likely to take health issues from poorly-bred parents on both sides, as those with well-bred healthy dogs are much less likely to cross-breed.
KC registration is no guarantee of all of careful breeding - but a non-KC registered dog is certainly far less likely to have been bred and reared with care. For a pedigree dog to be unregistered, it is likely that its mother is too young, too old, had too many puppies for more to be registered, or had some issue as a baby so a caring breeder 'limited' their registration.
NEVER take a puppy from horrible circumstances to 'rescue' it. All you are doing is paving the way for more to take its place. Hard though it is, it's better to walk away and report.
For my money, the best way to buy a puppy is to find a breeder of a pedigree breed who can demonstrate that they are in it for the right reasons - be that showing, agility, gundog work or whatever. Make sure they do the appropriate health tests for the breed (this bit is easy these days, look up breed clubs online and websites should tell you what is recommended) and don't accept excuses as to why they haven't been done. Once you have found a good breeder, be prepared to wait for a puppy for them.
Take your time and do it right - hopefully the result will be a healthy well-adjusted family member for about 15 years, so it's worth it.