I have some experience running a small domestic cleaning business in the past (but I don't offer this service anymore). For what its worth, I can give you a little advice that may be useful.
For some people a franchise might be the best option, but for most they probably are not value for money and will not give you a significant advantage in the market place. If you asked a 100 people at random in your area, I would wager hardly any of them would be able to name a single domestic cleaning business. Even the biggest domestic cleaning franchises do not have well known brand identities amongst the general public, so it's probably not worth paying for it.
Whether you choose to employ or subcontract your cleaners largely depends on the sort of domestic cleaning business you want to build. Cleaning agencies subcontract all of the work, they're not really cleaning businesses, they are marketing businesses that just happen to sell cleaning services. Most of the fees the client pays go to the cleaner, the rest is paid to the agency for managing the service ( VAT, if applicable, is then only usually applied to the agency fee not the cleaners fee). Bear in mind that many agencies tend to treat their cleaners as if they were employees. If you do this it is possible that your cleaners may try to claim rights as an employee and you may be forced to change their status and thus be liable for any tax and national insurance that should have been paid. When I ran my domestic business I mostly employed my cleaners and paid them significantly above the minimum wage. At the time, my fees were relatively high (compared to typical rates nowadays) so I was able to pay my staff well. If you want to employ and provide a good service you will probably need to charge in excess of £15 per hour (and possibly over £20 per hour). If you provide a good a reliable service and present it well, you don't need to compete on price and you will probably be able to charge a premium on typical rates.
I'm always happy to assist start-up cleaning business, please feel to ask me any further questions.