Adding Calculated Columns with data linked through 3 tables

SandeA 

See if this helps. Create the two columns in Request2 as below.

PrincipalSecurityName = 
VAR A = Request2[PrincipalSecurityUserId]
VAR B = CALCULATE(MAX(SecurityUser[UserId]),FILTER(ALL(SecurityUser),SecurityUser[SecurityUserId]=A))
RETURN CALCULATE(MAX(User[FullName]),FILTER(ALL(User),User[UserId]=B))

FulfillmentSecurityName = 
VAR A = Request2[FulfillmentSecurityUserId]
VAR B = CALCULATE(MAX(SecurityUser[UserId]),FILTER(ALL(SecurityUser),SecurityUser[SecurityUserId]=A))
RETURN CALCULATE(MAX(User[FullName]),FILTER(ALL(User),User[UserId]=B))

Based on the sample data, I got this output

Let us know.

Edit:

I am assuming the path is right

User[userid]-> securityuser(userid)  and securityuser(securityuserid) ->Reqest2(principalsecurityuserid)

User[userid]-> securityuser(userid)  and securityuser(securityuserid) ->Reqest2(Fullfilmentsecurityuserid)