Is that 5 adults? That requires an above average size car, especially if they have large cases.
Yes, you can get an automatic, they cost more. Automatics often are large cars only, but for you that is OK.
Where are you renting this car from (what town/location)? Do you intend to return it at the same location, or somewhere else? That decides what companies are available.
England to Wales is not an international border. This site confuses you by having separate sections for England, Wales and Scotland, but they are all the same country: United Kingdom.
I don't know where you come from (you don't say). Have you researched the other things to do with driving in the UK: Is your licence valid (do you need an International Driving Permit?), learn driving laws, learn road signs.