Google Sheets – How to Freeze Multiple Separate Rows

No, that isn't currently possible.

However, if the spreadsheet is used for viewing data (and not entering or modifying) you could make a new spreadsheet for each user, and use importRange from the "master" spreadsheet in each copy's "A1" cell. Each copy can then freeze/hide/filter as they please and their data will update almost in real-time as the master spreadsheet changes.
One dissadvantage is that you will lose some collaboration because making a cell comment etc will only be in each user's copy, so for adding comments or modifying you need to go to the master.

As a bonus, you can add an extra sheet on each of the copies and put a link to the master spreadsheet there so its easy to go to the master.

importRange : https://support.google.com/docs/answer/3093340?hl=en

To sort a query you simply have to wrap it in SORT.

=SORT(
    QUERY(
        {SheetOne!C3:F;SheetTwo!C3:F;SheetThree!F4:G;SheetFour!F4:G}
    )
    , 1, TRUE)

For example, the above formula takes the data from the sheets inside the query, and then sorts by ascending order from column 1.

This also works well to solve the problem of row splitting, where some rows get split up if you use different queries to pull from rows you intend to keep uniform.