BMW Family History (past and present):
1 Series - E87
3 Series - E46 Coupe, E46 M3, E90 (x3)
4 Series - F36, F82 M4
5 Series - E34 (x2), E39
7 Series - E32
X5 - E53, E70
X6 - E71
You're probably better selling and then buying individually IMO. Not very often you see a pair come up... and then even more unlikely that they will want to swap?
BMW Family History (past and present):
1 Series - E87
3 Series - E46 Coupe, E46 M3, E90 (x3)
4 Series - F36, F82 M4
5 Series - E34 (x2), E39
7 Series - E32
X5 - E53, E70
X6 - E71