If your goal is ios, android , and a website then if you don't necessarily want native code for the phone apps then you can use xamarian to make an app that will run on android and apple phones. Then for websites you could use asp.net. if you do that you could learn just one programming language: c#.
If you want native phone apps then you would need java for android , and swift for Apple. You could then make the website stuff (backend) with java.
Learning the languages isn't necessarily the hard part. The part you need to know are how to design stuff so that changing things in the future isn't a pain in the a.