How to pass the arraylist variable to the function in c#

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C#

Hi,I am new to c# ,I want to pass the Arraylist variable to the function CompareArrayList,But error is that 'input string is not in correct format' ,Can anyone tell me ,how to pass the arraylist variable to the function in c#, my code is below

protected void RelativeFamilyIDFrom(Double RelativeMemberID)
{
        sSQL = "SELECT AF_FamilyID FROM AllFamily_Master";
        sSQL = sSQL + " WHERE AF_MemberID IN('" + RelativeMemberID + "')";

        DS = new DataSet();
        da = new OdbcDataAdapter(sSQL,conn);
        da.Fill(DS);

        ArrayList list = new ArrayList();
        if (DS.Tables.Count > 0)
        {
            if (DS.Tables["table"].Rows.Count > 0)
            {
                for (int i = 0; i < DS.Tables["table"].Rows.Count; i++)
                {
                    allFamily[i] = Convert.ToDouble( DS.Tables["table"].Rows[i]["AF_FamilyID"].ToString());

                    list.Add(Convert.ToDouble(DS.Tables["table"].Rows[i]["AF_FamilyID"].ToString()));

                }
                CompareArrayList(list, Convert.ToDouble(lblUserToFamilyID.ToString()));
            }
        }
}

private bool CompareArrayList(ArrayList RelativeFamilyID,Double arr2)
{
        for (int i = 0; i < RelativeFamilyID.Count; i++)
        {
            if (!arr2.Equals(RelativeFamilyID[i]))
            return false;

        }
          return true;
}