Inquiries on fitting parent and child tables

[ThomasK1018]

Hi there. I am trying to sample data of two different transaction records based on the user ID, with both datasets containing repeating ID so I have created a third dataset that contains the unique user ID. I set the dataset with unique user ID as parent data. And I would like to know how can I link the two transaction record datasets to the parent data while also considering the intercorrelation between the two child tables? Should I build a sub child table that links to the child table or link both child tables to the parent table? Thanks.