Sql-server – Insert Into with Select works in once instance, but not the other. Subquery error or incorrect data

I am trying to write a script that will combine specific survey results based on the demographs used in the survey. I have been able to write a script that adds demographs together to create a new demograph e.g. M18+ and F18+ = A18+ which works perfectly however when trying to create a script that will create a demograph range e.g. A18-24, i am encountering some issues i cannot resolve.

My first script that adds two demographs together is as follows:

create table #SurveyTemp
(
    Com nchar(6),
    Survey nvarchar(50),
    Demo nchar(50),
    Wk int,
    Time int,
    Aud decimal(18,8)
);

insert into #SurveyTemp (Com, Survey, Demo, Wk, Time, Aud)
select   Com, Survey, 'A18+', Wk, Time, sum(Aud)
from     table_survey
where    survey = 'LO2017'
and      demograph like 'F18+'
or       surveyid = 'LO2017'
and      demograph like 'M18+'
group by Com, survey, Wk, Time:

insert into table_survey
select temp.Com, temp.Survey, temp.Demo, temp.Wk, temp.Time, temp.Aud
from   #SurveyTemp temp

drop table #SurveyTemp

This script works fine. It adds two demographs together and inserts new rows of data, creating a sum of the audience for each Com, Survey, Wk, and then Time. See the sample data set below where the addition of M18+ and F18+ has created a new record called A18+

Let me start with a sample data set:
(Disclaimer: the live database has MANY rows for each demograph)

com | surveyid | demo | wk | time | audience
-------------------------
 1 | LO2017    | A18+ | 1  | 300  |   4.7
 1 | LO2017    | F18+ | 1  | 300  |   1.9
 1 | LO2017    | M18+ | 1  | 300  |   2.8
 1 | LO2017    | A25+ | 1  | 300  |   2.3
 1 | LO2017    | A18+ | 2  | 100  |   3.7
 1 | LO2017    | F18+ | 2  | 100  |   1.9
 1 | LO2017    | M18+ | 2  | 100  |   2.8
 1 | LO2017    | A25+ | 2  | 100  |   4.3

What I need to write now is a script that creates a range. Notice how in the table above there is a A18+ and a A25+. Please bear in mind that in my live table there will be MULTIPLE rows for all demographs.

In this example, I will be using the above table. So, I need to create a similar script that will sum the audience for two demographs and then subtract one from the other to create a range. For example, subtract the A25+ data from A18+ to create a range called A1824. I hope that makes sense.

In the script below, I am trying to create a range called 'A1824' but I am either getting a "subquery returned more than 1 row" error OR it is inserting the wrong data into the temp table where the sum in AudOne and AudTwo is the SAME for every single Wk and Time.

create table #SurveyTemp
(
    Com nchar(6),
    Survey nvarchar(50),
    Demo nchar(50),
    Wk int,
    Time int,
    Aud decimal(18,8),
    AudOne decimal(18,8),
    AudTwo decimal(18,8)
);

insert into #SurveyTemp (Com, Survey, Demo, Wk, TimeBlock, Aud, AudOne, AudTwo)
(select   Com, Survey, 'A1824', Wk, Time, 0.0, 
          (select sum(aud) from table_survey where demo = 'A18+'), 
          (select sum(aud) from table_survey where demo = 'A25+')
 from     table_survey 
 where    surveyid = 'LO2017'
 group by Com, survey, Wk, Time, 
)

update #SurveyTemp
set Aud = AudOne - AudTwo;

insert into table_survey
select temp.Com, temp.survey, temp.demo, temp.Wk, temp.Time, temp.aud
from   #SurveyTemp temp

drop table #SurveyTemp

It is this second script that i need to get working and have spent hours trying to resolve without much luck.
Please let me know if i can provide any more information to help you help me!

Edit:
My expected results would be something like the following:

com | surveyid | demo  | wk | time | audience
-------------------------
 1  | LO2017   | A1824 | 1  | 300  |   2.4

But there would be multiple rows where there are multiple 'wk' and 'time' entries. E.g.:

com | surveyid | demo  | wk | time | audience
-------------------------
 1  | LO2017   | A1824 | 1  | 100  |   2.4
 1  | LO2017   | A1824 | 1  | 200  |   3.7
 1  | LO2017   | A1824 | 2  | 100  |   2.1
 1  | LO2017   | A1824 | 2  | 200  |   6.2