You have a many to many relationship. A participant can invest in many investments and a given investment can have many participants.
Participants::__pkParticipantID = Participant_Investment::_fkParticipantID
Investments::__pkInvestmentID = Participant_Investment::_fkInvestmentID
You can place a portal to Participant_Investment on the Participants layout to list and select Investments records for each given Participants record. Fields from Investments can be included in the Portal to show additional info about each selected Investments record and the _fkInvestmentID field can be set up with a value list for selecting Investments records by their ID field.
Note that information specific to a given participant's investment can be recorded in fields of this added "join" table. And layouts based on the join table can be used to set up summary reports reporting the investment details for one or more participants and for one or more investments.
For an explanation of the notation that I am using, see the first post of: Common Forum Relationship and Field Notations Explained
I was able to easily import the members and their personal information. The problem I'm having now is how to import the investments and the balance to work with with this solution. I know its probably staring me in the face but unfortunately I'm not seeing it :/.
The key to importing the investment is the field that links these to the members. Using spreadsheet data I was able to create a table of vendors. I wanted to see expense reports paid for employees (as selected vendors). When I imported the transactions, both tables have the VendorID present. This linked the two tables, and the checks showed in the vendor-invoice portal.