DBGrid Tquery SQL problem

My question/s is as follows

If on the same form/page/window with components for  3 Tables
If I have DBEdit components for Vendor - TTable eg Company Name in TOP
LEFT CORNER with DBNav for Table-Vendor
      DBEdit components for InvIdx -TTable eg Invoice Number in TOP
RIGHT CORNER with DBNav for Table-InvIdx
      and a
      DBGrid In the lower half of the screen for Invoice -TTable with

Question 1
How would I get the DBGrid USING TQuery SQL to show/filter  for the

  OrderNo   InvIdx VendorNo  LineItem PartNo Description Qty UnitPrice
TotalPrice Paid Balance
 103              1         Delta              1          1098
Gauze        10   1.97          19.70     0         19.70
 104              1         Delta              2            209
Saline          2   5.60          11.20     0         11.20

      What TQuery SQL code would I use on the DBGRID for Invoice Table
so that it only looks at the entries
      which are concurrent  for  InvIdx{Invoice Number} and VendorNo
{CompanyName} ?????

Questio 2
How to make SPECIAL(IF POSSIBLE) DBNav for Table- Invoice to scroll/MOVE
ON NEXT 'LineItem'
linked to InvIdx even though the index/key field is "OrderNo"

This is what I would like using Paradox 7 tables in Delphi 5

three main tables plus a parts table etc

1.Vendor TTable{for company seller/vendor details}

VendorNo   N   *
CompanyName  A 40
plus other fields as required

2.InvIdx TTable {for indexing individual invoices by invoice number}

InvIdx   N  *
InvoiceNo  A 15 *
No other fields

3. Invoice TTable
OrderNo    N  *
InvIdx   N
VendorNo  N
OrderDate  D
LineItem   N
PartNo   N
Description  A 40
Qty    N
UnitPrice   $
TotalPrice   ${calc}
Paid    $
Balance   ${calc}