Sounds like the wax gasket is leaking or a crack in the bowl. Is the floor dry.
You cannot. It has to be snaked out or the toliet bowl replaced.
It's not the toilet, there's a blockage in the pipes some where after the drain pipe from the toilet joins up with the drain pipe from the tub.You're going to need to have the pipe snaked.
They have probably got air bubbles in them. It may be a worn out ballcock at a toilet.
You may need to replace the wax seal under the toilet.
You have to use toilet more
Mainline stoppage.
You should get your drain lines snaked
Firstly, you have a anti syphon problem, this is causing the drainage and the bubbles are caused by a possible blockage in your main sewer line.
Bubbles in the tank when flushing the toilet can be a sign of a faulty flapper not sealing properly. This can lead to air entering the tank, creating bubbles. Check the flapper for damage or misalignment and replace if needed to fix the issue.
Sounds like the washing machine discharge is fitted to the main drain in the wrong place and it's discharge is filling your toilet. It's possible there may be something of a blockage just after the toilet, causing a backup. I would try to snake the the pipe from toilet out. You may even have to remove the toilet from the floor and do it there if there is no access underneath (like a basement or a crawlspace). I have snaked main drains from the toilets many times, and it's a pain having to re-re the toilet, but often it's the only way.
When you flush the toilet, the rapid movement of water creates turbulence that can disturb any trapped air bubbles. These bubbles can rise to the surface and be released into the water, creating the appearance of small bubbles flowing into the toilet. It is a natural consequence of the flushing process.