Setting planes to escort mode and setting 'the escort target' so squad2 escorts squad1, and squad3 escorts squad2 is the only 'ingame' way that semi works- and this has several limitations, height separation is ~ 1500m and escorting units can end up strung out behind. (something like Frog's formation mod would be handy
)
Usually I make up groups 'manually', adding a unit at a time and checking speeds/ positions on playing through. somewhat time consuming
particularly as you have to reduce speed of higher units to match formation speed- setting in fmb is IAS so if 2nd squad is 300m higher than the first, 2nd squads speed is~3km/h slower.
'crossover' turns are 'fun'
5 AC kette is possible- if unit is set as a stuka formation. This is not an ideal way but may work for some purposes