Yes three categories of foot (retinue, Militia and Welsh) can form longbows and bill/spear in mixed order.
Going to have to get more Archers now!
Which raises another question (sorry)
Can the mixed units use stakes? As the archers can buy them. If so do all the bases in the unit buy them or just the archers?
My guess is yes. As there is a minimum of 50% archers in a mixed order Unit?
And why are stakes cheeper for the close order than the open order?