BGP advertising same networks on 2 ISP independently (without iBGP)

I am new to BGP. We have established BGP neighborship with 2 uplink providers advertising different networks and receiving default routes from both using same AS number. We couldn’t establish iBGP as we have a requirement to use both ISP A and ISP B for specific networks to reach to internet.

  • Network A should prefer ISP A for incoming and outgoing
  • Network B should prefer ISP B for incoming and outgoing
  • Network C should prefer ISP B but in case ISP B goes down should prefer ISP A
    Please advise

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