Re the ise/ize matter, the old rule - and one still largely followed by The Oxford English Dictionary - was that words derived from classical Greek with the letter zeta in their suffix were rendered ize in English...ie retained the ‘z'. However, many modern publishers - including The Times newspaper - prefer the Latinate and more modern ise for most such words. Thus, normal British usage has realise, organise, apologise and so on.
Certain words - eg capsize - are never modified to have an ise ending. In the same way, there are others - such as disguise, analyse, circumcise, televise - which are never given an ize ending. Apart from the exceptions mentioned above, you are basically free to use whichever form - ise/ize - you prefer! Only...be consistent.
I hope you get your spell-checker modified successfully.