I'm not sure i understand at 100% your problem, but, let me try,
the key field connecting your table "order" to your table "person" may be "CustomerID" and also may be "SellerID" ?
If it is the case, you can try a composite Key, by concatenating these two fields like this:
CustomerID &'-'& SellerID as PersonKey (on the order table)
and do the same on the Person table.
let me know
I Think you want to connect Person and Seller table to the fact table. If it is right the try below logic.
(ooxml, embedded labels, table is [Table 1]);
Applymap('_MappingTable',"PersonID",'NA') AS PersonName,
Applymap('_MappingTable',"SellerID",'NA') AS SellerName
(ooxml, embedded labels, table is [Table 2]);
Hopefully, this will helpfull to you.