Code efficiency with many records
Concatenating an splitting seems like you're making extra work for yourself.  I suggest summing the results of a string-to-integer translation.

from collections import defaultdict

_RISK_SCORE = defaultdict(int, [('Extreme Risk', 3), ('High Risk', 2), ('At Risk', 1)])

@property
def risk_status(self):
    """ This function assigns numeric weight to risks. It returns an overall integer score. """
    return sum(self._RISK_SCORE[r] for r in (
        self.si_risk,
        self.aggbs_risk,
        self.cfimb_risk,
        self.cfiab_risk,
        self.cei_risk,
    ))