I want to turn down a job offer my family wants me to take.

I'll try to keep the story brief.

I turned eighteen last month, I'm a freshman at Uni, and never had a job before because I was focused on getting a scholarship during high school via extra-curricular activities, creative clubs, and competitive sports. freshman at uni, and I've been completing multiple work placements as per the course requirements.

For the past six months, since after completing a work placement there, I've been volunteering at a place I won't name because I'm going to complain in-depth about the management.

This place is fairly well known, attracts a lot of business and has a good reputation in its industry. If you work there or volunteer there, it's the type of place that makes your resume look good.

I enjoy volunteering there, I go when I can and stay for as long as I can.
It's flexiable, the employees are nice, and the work is satisfying.

While I was doing my placement at this place, I pretty much ruled out the idea of ever working for them as an employee. I like volunteering there, but it's a very different thing to work there.

The reason: bad management.

In just under three months, four perfectly good employees have left due to the bad management team. During my time as a student and as a volunteer, I have watched people being pushed to the edge until they can't take it anymore and finally quit.

It's gotten to the point where out of an original team of ten, there are now only two employees left that have been working under this manager for longer than a year, staying only because they're passionate about the industry.

Thankfully, since I'm a volunteer, I'm a free helping hand that they need, so the volunteers rarely get shouted at as badly, which is my saving grace on the days that I volunteer.

So, what exactly sucks about the management?
The first thing is that the rosters they send out never make any sense or even align properly with the employee's scheduled hours or their specialisation. This means that people whose shift ends earlier, sometimes get rostered on as the closing team, meaning they're pretty much stuck there all day.

This happens consistently, to the point where the manager (Call him Fred) gets upset about it, but he never does anything to fix it, like talk to the other manager in charge of rostering.

The second thing is Fred's entire presence there.
Let me give you a short list of things Fred has done.
1. Taken 3 weeks off of work without telling any of his employees.
2. Shouted and threatened to write up reports about employees walking dirt into the main room and not cleaning it up until the end of the shift (Which is unavoidable, this job is very outdoorsy, and it's impossible to clean it before the end of the shift because everyone's running around doing far more important things.)
3. Speaks condescendingly, has a short fuse and absolutely refuses ideas that any ideas could improve the place because they're "not big enough issues." (Yet the dirt is.)
4. Constantly arrives late and then yells at his employees who have been waiting for him to arrive about being late.
5. Refuses to call one of his employees by the name she changed to (following some traumatic experiences with her family) and goes as far as to introduce her with her old name.

This is just a short list, I can think of at least 10 more times, but I don't want this post to be too long.

As you can see, being an employee there sucks, and you have to be as patient as a saint or love your job to hell to stay.

This is where that job offer comes in again.
Four employees quitting kind of opened a few windows, and they decided to ask me if I wanted to temporarily fill in since I'd been there for a while already.

As I said before, I'm a uni student who also does placements, and has days where I need to attend classes.
So, after being offered, I tried to negotiate what a timetable might look like, and Fred just became irritated and grumbled, "Just don't show up on those days then," and walked off before I could say anything else.

Here's why this doesn't work in my situation:
Fred wants me to work 5 days (Monday, Wednesday, Friday, Saturday, Sunday.)
The issue with this is that only leaves 2 days free to do my placement, which doesn't even work then because those 2 days are also the days that I have classes. This would leave me chosen between classes and placement, and I'd pretty much have 0 days off for 6 months straight.
On top of all this, I still have to turn in assignments, complete exams and finish homework.

I thought it over and weighed the pros and cons.

Here are the pros;
1. Looks good on a resume.
2. 6 months of fairly decent pay.
3. I already like the jobs I do there and know how to do them
4. It's in an industry relevant to my course.

Here are the cons;
1. Stressful toxic work environment.
2. I'd have to balance uni work, placement work and then working at this place, leaving me with 0 days off for 6 whole months.
3. I already don't get along with the manager.
4. I've never been interested in starting here as an employee there, and I don't see a future continuing as an employee with the company.

So I don't want the job.

My family, however, really does want me to take it.
When I told them I was offered a job (big mistake) they were ecstatic, congratulating me and telling me how proud they are.
Not once did they ask me if I was going to take it or not or how i felt.
They just assumed I wanted it, and to be fair, that's because i don't tell them all the shitty things going on behind the scene, because I didn't want them to think that I hated going there.

So to them, this looks like a dream job.

And although I can't deny it's a massive opportunity, I just don't think the sacrifices I'd have to make for it is a good trade-off for a job that I don't plan on continuing after the initial six months.

The thing is, I have no idea how to break this to my family, who are so happy for me that they hugged me when they found out.

I'm worried that they'll say I should just "suck it up" because it's a good opportunity and looks impressive on a resume or that they'll think it's because I don't want a job, which isn't true; I've been looking for nightshift jobs since those more adequately suit my timetable.
I don't want to disappoint them, and it's to the point where I'm almost considering lying and saying that the place rescinded the offer.

How can I tell them all of this? Or should I just lie.