You have a grinder pump that boosts the sewage up to the main floor to enter the drain system. The float in this pump system is not working correctly and the standing water level in the tank is too high. Adjust the float, it will cure your issue.
Most Likely, your pipes are all hooked up in the same system. all the pipes travel to the basement most likely.
because the upstairs toilet drain was clogged up.
partially clogged drain or vent, improperly installed vent or drain
It is quite possible that your main pipe to the city sewer system has become blocked somewhere between the basement floor drain and the man city sewer line. Could be a result of items flushed down the toilet(s), or damaged pipes as a result of age, tree roots searching for water, etc. Suggest having your main access to the city sewer system checked by camera.
Have a plumber snake out your drains.ANS 2 - Install a flapper valve section on the sink drain pipe so water can go down but not up - cheap and very easy to do.
You have a blockage in your main sewerline. You have a problem with your venting system. This is why some codes now require a vent within 6" of the toilet. If you will add a vvent to your main line at the toilet you will stop this. Check to make sure your vents are not clogged by a bird or bees nest first.
There is a main drain that runs from the basement through the roof where it is the vent for the system. If you look at the layout of the house, the upstairs bath is most likely over the downstairs one or the kitchen. If you look on the roof, you will see a 4 inch pipe coming through the roof that should be over the upstairs bath. The sink and shower drain into that and then to the basement and out of the house. Most likely the main stack is in the wall behind the toilet.
First thing you should do is call a plumber. Drain lines are not supposed to leak. Your drain line is clogged and needs to be snaked out and the leaking pipe repaired.
If the drain is adequate size, 3inch, then you could.
Maximum distance of the toilet to the drain is 6 metres (20 feet). The angle of drop is set by the branch at 112 1/2o, which equates to about 1/4" of drop per foot.
The drain from the toilet to the main drain is plugged and the branch to the shower is not. If the main floor toilet flushes, it is between the two toilets and not between the house and the sewer.
What you probably need to do is snake out the vents. You probably have debris in them.1- you may have a slight blockage2- Poor venting and water Jetting will scour the piping rather then rodding
The drain is plugged somewhat between the upstairs and downstairs. Need to snake the drains.