Common part for multi subcontractor

Dear Experts,

Here is the scenario,

We purchased common part A from vendor X by schedule agreement, and delivery material A to venodr Y and vendor Z for subcontracting.

Vendor Y, semifinish good B:A, BOM: 1:1;

Vendor Z, another semifinish good C:A, BOM: 1:2

Let's make an example for my requirement,

requirement for semi B, 1 PC while 2 PC for semi C,

The total requirement for A should be 5 PC, the material A is packed as 3 PC per box from vendor X, and in our plant we will not do any unpacking for this material, we directly ship it to subcontractor.

Here is the question, according to the MRP result, we will get 6PC(2 Box) once we setup min lot size 3PC; but it will be a problem, since the requirement for vendor Y is 1 pc, 1 box needed, vendor Z, 4PC, 2 box is needed.

Any solution for this?

Thanks in advance.