A Guardian is a person who is appointed or legally responsible for taking care of persons who are unable to take care of themselves due to age (ie minors, normally until they become major) or unsound mind etc. Obviously, a Guardian must not be a minor or a person of unsound mind. You may appoint a Trustee who is different from a Guardian of your children, if you believe that the Guardian may not have the skills to manage your assets.
In general, a Guardian for Asset is responsible for managing the assets and applying them for the benefit of persons (who could be minors or incapacitated) or causes listed in the Will.
A trustee is an individual or a member of a board that is given powers to manage a asset in trust with a legal obligation to manage or administer it solely for the purpose specified.
In general, a Guardian is responsible more for physically taking care of persons who are minors or incapacitated. A Guardian for Asset is responsible more for managing the assets and applying them for the benefit of persons or causes listed in the Will.
A right of asset held by someone for the benefit of another. A person who creates the Trust is called the author of the Trust. You (author) can create a Trust of a asset (subject matter of a Trust) to be managed by Y (Trustee) and to be applied for the benefit of X (Beneficiary). The document by which a Trust is declared is called an Instrument of Trust. There is a separate law in India that regulates trusts.