I'm currently working on english social classes in the early 19th century, and wondered: was aristocracy including royal members, or only gentry + peers?
I would suggest the answer is "No" - and the aristocracy would not actually include gentry either. Social gradations at that time were subtle but strong, a wealthy "gentleman" would still defer to a peer, even if the peer were the poorer. Read Jane Austen and Anthony Trollope for examples. But royalty was in a different category, as, indeed, it is today; the tabloids might titter if a Duke were caught in a compromising position, but it would not be the headline news that a royal scandal would provoke. Also - and I stand to be corrected on this - the aristocracy's influence came from land (vast holdings in many cases) industry (they weren't above exploiting coal or other resources) and their power of patronage. Royals, to the best of my knowledge, lacked the first two - Parliament frequently was asked to bail out profligate Princes! And - a final touchstone - would a Duke, say, challenge a prince to a duel (rare occurrences but not unknown)? The answer is almost certainly not, such an act would be treasonable.
This question should probably be closed as opinion based, particularly given the lack of prelimnary research. There is no clearly and objectively acceptable answer. I'm reluctant to contradict TheHonRose, but from my perspective, the fundamental division of society is between the aristocrats and the common folk. Royals are clearly part of the aristocracy.
Within the aristocracy the royalty are recognized as distinct from the "ordinary" aristocracy, and the gentry are generally also recognized as distinct.
Ultimately though I think the terms are imprecise, and it isn't possible to answer without context. If a cab driver refers to the Prince of Wales as "an aristocrat", nobody will be confused. If the Marquis Rippon were to refer to the same individual by the same term, it might cause confusion. There are no simple answers.
This depends on how you define the word aristocracy. Its not a legal term or anything, just a convenient categorization. Havng said that, 19th century writings refer to Britain's aristocracy and royalty distinctly. Most of the time, the two are just too different to be lumped together in descriptions. Aristocracy is usually considered below the royals today too.
Besides, "the rest of the nobility or aristocracy" is a mouthful.