Regarding the fact that a company is made up of people and we use who for people, is it proper to use who here?
A company is normally, but not invariably, treated as inanimate, so it will be a company which makes or a company that makes, when the relative clause is integrated (also known as ‘defining’ or ‘restrictive’). When the relative clause is supplementary (also known as ‘non-defining’ or ‘non-restrictive’), it is normally introduced by which.
This means that we can say XYZ Inc. is a company that makes high tensile steel or we can say XYZ Inc. is a company which makes high tensile steel. But we generally say XYZ Inc., which makes high tensile steel, has had poor results this year rather than XYZ Inc., that makes high tensile steel, has had poor results this year. Some people claim that you cannot use which to introduce an integrated relative clause, but they are wrong.
(There is a further complication with a word like company, which is seen variously as singular and plural. For the sake of simplicity, I have treated it here as singular.)