It could be possible they ask about money where its comes from if you show an account with 100 trillion dollars.
As long as you are showing money with regulerize and authentic bank or financial institution of any country, there is no question where this money came from as it is a responsibility of that bank of financial instituion and they already have asked that question in account opening process. Usually financial sponsor write about the source of income in there letter of financial consent / Affadavit of support. It may be depened upon the finacial sponsor location as well.
About legal guardian, if they are other than your parents, you need to show a court document + letter of financial consent as specified by UKBA maintenance guide for Teir 4. A lawyer can provide you better help in this regards.