As a first pass:

Europe
FRA, 11: AA, BA, CX, AY, IB, JL, LA, MA, QF, RJ, S7 (AB; the only I can think of with all active members)
LHR, 8: AA, BA, CX, AY, IB, JL, QF, RJ (IT)
MAD, 8: AA, BA, AY, IB, LA, MA, RJ, S7 (AB)
CDG, 8: AA, BA, CX, AY, JL, LA, MA, RJ (HG)

Americas
JFK, 9: AA, BA, CX, AY, IB, JL, LA, QF, RJ (AB)
LAX, 7: AA, BA, CX, IB, JL, LA, QF (AB)
ORD, 6: AA, BA, CX, IB, JL, RJ

Asia Pacific
HKG, 6: BA, CX, AY, JL, QF, RJ (IT)
NRT, 6: AA, BA, CX, AY, JL, QF
SYD, 5: BA, CX, JL, LA, QF