Hi Den and welcome to our forums,
I too have heard that ms are fazing out windows 7...(gulp)
Microsoft are not fazing out Win 7..... but updates and security patches to the operating system will not be available from next week, so it would be correct to say that from then on it will not be given support by Microsoft.
Your computer will still continue to work but will become more vulnerable to infection if it is exposed to other data sources ( the Internet for example) so if you wish to continue using it then it will be Ok if not allowed to come into contact with other data sources, and your spreadsheets should be Ok.
If however you intend to, for example, use the computer for accessing the Internet then you will need to take careful precautions to try and ensure that your computer remains clear of infections/malicious code. As an absolute minimum make sure that your back up copies of everything that is important to you on your computer is 100% accurate, comprehensive, and verified to work!...
Check your disc images to make sure they are kept up to date and are reliable.... if you have any doubts then use something like, Macrium Reflect Free to take fresh disc images, make the emergency boot disc and keep several copies of your images with at least one kept safe offsite. A few external hard drives will come in handy here but don't keep them connected (plugged in) unless you are actually using them.
Your spreadsheets should work Ok if you decide you want to use Win 10 at some time,
Sorry I cannot help with your tablet and android operating system..... Maybe some other of our members know about these and will chime in.