Half of house not draining properly

[Skinny]

I have a large raised ranch house with a partially finished basement. The basement plumbing works just fine, everything flows to the sump pit and the sewage ejector pump works just fine, also. Now the upstairs is where the issue lies. On one half of the upstairs is just the master bath, that drains just fine. On the other half of the home the drain line has the kitchen sink and dishwasher, a utility sink, the washer, bathtub, bathroom sink, and toilet. The water seems to flow just fine. However, we have a 9 year old girl and 7 year old boy that go through a lot of toilet paper. The toilet will take pee down no problem, but after a few solids the toilet would plug. I noticed plunging the toilet that sometimes the water would come up in the shower. I had the drain cleaned by a professional with a power snake. Worked great for a few days, started plugging again, had him come out again. He did it again. Worked great for a few days. He said I should look into getting the plumbing redone down the line due to the bad angles. So I ask, what would my best option be here...

I believe this is the fitting he thinks needs to be changed.

Here is the 4" 90 to the T fitting. The 6" line goes to the left about 2 to 3 feet and then goes to the down pipe that goes out to the holding tank.

Should I change the 90 to a long turn and do something with the T fitting? Should shorten up the main 4" line and take it right to the 6" down pipe? I'm just not sure. Also, I checked the slope, at the toilet its approximately 102" and the 90 is at about 92" with the T being at 90". Any help would be appreciated. If more details or images are necessary, let me know!

 

[Reach4]

Not to say your drains don't need fixing, but I would also consider a bidet attachment for the problem toilet. The paper usage would probably go down a lot.

 

[Sponsor]

 

[Skinny]

Not to say your drains don't need fixing, but I would also consider a bidet attachment for the problem toilet. The paper usage would probably go down a lot.

That's probably a pretty good idea. I have never used one, along with everyone in the house, but I'm sure we could get used to it.

 

[Terry]

Install a combo or wye with 45 where the santee is now. Use a long sweep 90 in the other location.
For paper, you may want to consider something other than Charmin. How old is the toilet? Some of the newer ones use a 3" flush valve that gives you a good charge down the line as the water leaves the bowl much quicker.
You don't show the fitting where the toilet enters the line, but that should be a combo too. A santee on it's side allows the paper and poo to go both directions. Not a good thing.

 

[Skinny]

Sorry it took so long to respond. What is wrong with Charmin toilet paper? and how did you know I use Charmin, haha. The toilet is probably from when the house was built, 2004. And yes, the toilet also has a santee fitting.