Just for comparison, in year 1 my DC in a private (non London) prep school would get as many or as few books each week as they were capable of reading (for us that was 2) and we were encouraged to read every day but it was not a requirement. We also got a book to be read to them once a week. There would be 6-8 spellings to learn each week. Examples of easier ones: said, there, which, little, before, should. Middling ones: denial, because, difficult, through, sentence, elephant, however spellings are differentiated within the year group and I don't think my DC gets any of the harder ones so I can't comment on those. There is also optional holiday work, which apparently most parents do a bit of every day!
I should point out though that the school is very play focused and big on co / extra curricular and sports, so only 2 1/2 hours a day were 'academic' lessons and the rest were music, art, sports, swimming, outdoor school etc.
It sounds to me like a lot of your DC's have a lot of homework for year 1 compared to my DC!