You would need three pips - even if they all are heading to the same direction.
In fact it would probably be more than that.
Look at PIP Expenditure on page 27 of the rules.
1 PIP is expended for each halt by...a group including impetuous troops.Then, go down the page.
1 extra PIP is expended by...a halt...(e) If a...land...group includes any irregulars...and...[third dot point] halts to prevent spontaneous advance...So to halt a group of spontaneous irregulars (with a few exceptions) costs 2 PIPs. If your group of six elements went impetuous last turn and is now three separate columns, that's going to be
six PIPs to halt them in place.
Given the difficulty of getting impetuous troops back under control, you either work really hard to keep them under control as long as possible, or you build your plans around letting them go impetuous. (The second idea isn't necessarily a bad thing, as impetuous Wb (F) who don't contact enemy move as fast as LH (O), so you can cover a lot of ground without spending PIPs.)