Jason, my first question is: Why does this all need to be in the same table? This probably will be simpler if you have a related table to handle trusts and decedents. If you are still going to use one table then at a minimum you will need to add a record type field to the table and also at least two other foreign key fields. I will use your example above to illustrate.
A1 Client 1 ID =01234 RecType = Master IDF_Trust = empty, IDF_Decedent = empty
A2 Client 2 ID =02345 RecType = Master IDF_Trust = empty, IDF_Decedent = empty
A3 Trust 1 ID = 23456 RecType = Trust IDF_Trust = 01234, IDF_Decedent = empty
A4 Client Decedent 1 ID = 45667 RecType = Decedent IDF_Trust = empty, IDF_Decedent = 01234
Your layout would display only Master record type and the portal in that layout would display Trust and Decedent records.With the foreign keys you have the ability to relate (even if it is a self relation) back to the master file. You could probably make this work with just one foreign key instead of one for each type of record. Also make sure your keys are arbitrary. Not based on any type of data. Some of the solutions I have created I've started using the Get(uuid) function as a key generator.
I hope this helps.