the real question is where do you want to put the files, you could put them on onedrive, dropbox or similar, in which case everything can use them and you have no sync issues as they are all in the same place. You could use the home group feature, BUT it requires that the machine that 'hosts' the files is always on (whilst you want to access them anyway). The i-device ruins the latter option, office 365 might therefore work as it is setup to deal with cloud really easily, I think that one license covers a desktop and a mobile device, check the licensing.