Did you already create the Tables in Dataverse?
There are many ways to do this, and depends on which choices makes the most sense for your business.
Its not really that many rows, which is good.
Dataflows:
Allows you to configure a connection to the other system and import the data after mapping it
There is another good option.
If you create the Tables in Dataverse 1st. Setup the relationships between the tables.
You can build a customize bulk import. the reason I say custom is because your files, would have at best a 2ndary key, not a primary key in Dataverse, which is a guid, so a custom run what it does is
Inserts the parent
Inserts the Child
Associate the Child to the Parent
But that has to be implemented as you build the custom mapping.
You can also build your own using the Dataverse SDS, where you could grab the data from DB2, then insert it directly into Dataverse and then associate the records yourself in your code. Its quite simple.
Image code like this (Pseudo of course)
Insert into Dataverse and get back the Parent GUID
Insert into ChildA using the GUID from the previous step to build the Parent child relationship
Insert into ChildB using the GUID from the previous step to build the Parent child relationship
Power Automate
You can build a flow, that would grab the data from DB2 and perform the actions I spoke of in the previous (Build your own) option.
It would literally
Loop through your DB2 parent
Create and get GUID
Create ChildA and Associate to Parent
Create ChildB and Associate to Parent
Please let me know if you need more help.
If this helps you, Please Mark as such and maybe a Like :-)
Thanks!