Hi, welcome to Sitepoint
I think we may need to see a couple of examples with data in the columns so that we can suggest something suitable.
At the moment the inner elements won't force a scrollbar because they have no width in which to contain something. The only way a scrollbar would work in your structure was if it was on the parent.
<div style="border:1px solid gray;padding:10px;overflow-x:scroll">
<fieldset style="border:1px solid gray;border-radius:5px">
If you don't control the overflow on the parent then it will just collapse and will not be held open by a child of greater width unless you set a min-width equal to the largest fixed width element inside.
I'd really need to see examples of the data in the various columns to suggest anything better as I may be barking up the wrong tree:)