The line concept in form builder can be a bit difficult.
I guess, think in terms of tables and nested tables.
each line is a table row.
the sets are a nested table inside the line table, each set is a new table row.
for all three to be on the same physical line, they must be in the same set.
Sets do not share the same validation, they share the same validation *error message*
For the checkbox group, if you set the size to One Column, they should each be on a separate line, and the labels should line up correctly. Since CSS form builder uses CSS for positioning the elements, it is possible that you have CSS on you page that is conflicting.
If you are having a different experience with the positioning of elements, I really need to see the issue in the browser to troubleshoot it.
When using a menu or list, the Required validation is used if you have a blank value at the top:
Make a selection
and what to ensure a selection is made.
The Invalid Value option allows you to offer a selection in the list, but refuse the form to submit if that option is selected.
The option to have a single radio button is left out because you should use a checkbox instead in that scenario, A single radio button makes no sense.
A radio button is really intended to be tied into a group.
The job of a radio button is to offer multiple options, but only allow one to be checked.
