NHS for non resident UK citizen

My sister is UK citizen but she have never lived in the UK (only some visits now and then), Is she entitled for NHS services or not? I heard that non residents are not entitled. Let's say she'll visit England just to register herself and her children with some GP, what does it take to do this? She doesn't have an IN, doesn't own a uk property, doesn't have a UK bank account, so Passports are the only thing she and her children have to do with the UK, What benefits can they get besides NHS (if that's possible at all), She's planning to move to England gradually over 3-4 years time, she's wondering if she can get her children into schools for free, if there's any summer schools or something because they'd need some time to learn enlgish before she can permanently move here. She keeps asking me about what benefits they can get and I have looked on the internet but couldn't find anything. I know this is not an immigration issue but I'm sure many seniors here would be able to help.

Thanks

No, she's not really. In short, the NHS is for residents of the UK, not citizens specifically. (Indeed, despite near-hysterical reports from time to time in various tabloid newspapers about British citizens living overseas being denied NHS treatment, it has always been thus from the day that the NHS was founded.) Confusion arises in part because the rules aren't always properly enforced, and also because a British citizen is eligible for NHS treatment if he or she starts to live in the UK: the question with respect to a recently arrived citizen who has hitherto lived somewhere else is what constitutes "living" in the UK! In part it has to do with intentions, and visiting the UK, with or without the purpose of registering with a doctor, is not indicative of coming to the UK to live, I guess.

Many doctors surgeries (with a vigilant receptionist) now insist on proof of permanent address in the UK...utility or council tax bill + passport for example. We even had to produce this when we moved house and had previously been registered with a doctor in another town. I'm British and my husband is Non-Eu...but it was the same for both of us.