How can the releases/shipments to be consolidate into a single shipment. 

Answer

This can be achieved through createShipment Api or through ConsoidateToShipment Api.

ConsolidateToShipment:

In the consolidateToShipemnt Api, pass the same shipment number each when the call is made to the Api. By doing this many orders are consolidated to a single shipment.

Input XML:
 
<OrderRelease  DoNotConsolidate="" DocumentType="0001" EnterpriseCode="DEFAULT" OrderAvailableOnSystem="" OrderHeaderKey="2009111318335248984" OrderNo="Y100000280" OrderReleaseKey="2009111318342649000" ShipNode="Node" ShipmentConsolidationGroupId="" ShipmentKey="" ShipmentNo="ABC">
 <OrderLines>
 <OrderLine  OrderedQty="10" PrimeLineNo="1" SubLineNo="1">
  <Item ItemID="item" ProductClass="" UnitOfMeasure="EACH" />
  <PersonInfoMarkFor Country="US"  />
</OrderLine>
  </OrderLines>
  <ToAddress   Country="US"/>
  <FromAddress   Country="US"/>
  <MarkForAddress  Country="US"/>
 </OrderRelease>

 CreateShipment:

CreateShipment will create a single shipment for many orders.

 <Shipment Action="Create" DocumentType="0001" IgnoreOrdering="Y">
    <OrderReleases>
        <OrderRelease AssociationAction="Add" OrderHeaderKey="2009101515243038916" ReleaseNo="1"/>
        <OrderRelease AssociationAction="Add" OrderHeaderKey="2009101514493838525" ReleaseNo="1"/>
    </OrderReleases>
</Shipment>