Retrieve related records in lookup using Odata query and filter based on another entity

Hi,

I have to work on scenario to display records :

Scenario:

Entity 1 --> Where we have to show records in a Payer lookup field based on Child Contact look up field.

Entity 2 --> Child Contact (Contact)

Entity 3 --> Connections (this entity will be used to filter contact records)

Description: OnLoad of Entity 1 form there is a lookup named Child based on which i have to show Connections whose connection role = Parent in Payer lookup field.

Please let me know best practice to achieve this scenario.

Thanks in Advance.