OBS just runs multipli ones without me wanting it too
That's impossible. Whenever OBS starts, if it detects a 2nd+ instance a message pops up to let you know that. On said message screen is a checkbox that tells OBS to not show the message again, which has to be checked by the user (i.e. you) so it doesn't show up anymore.
To deal with the double+ instances of OBS running, open Task Manager (Ctrl+Shift+Esc), select the "More Details" option at the bottom and then look in the background processes for OBS. Right-click on it and select "End Task". Make sure all instances of OBS are closed, then start OBS.
As to crashes and general instability, I can see from your log that you're running Avast, which is know to interfere with OBS. You need to contact them on how to setup Avast so its doesn't interfere with OBS.
Additionally in the log you posted I see either 4 webcams (all Logitech C920s?) or 1 webcam being added 4 times as different devices. If you only have one Webcam, then remove it completely from all scenes and add it to your first scene. Then when you want to add it to another scene select "Add->Video Capture Device->Add Existing->[Select the C920 you already added]."
If you actually have 4 c920s, then you're running into an issue with Logitech and them not supporting multiple devices by having unique IDs for programs like OBS to identify which webcam is which. Please contact Logitech and express your displeasure at their laziness.
As to the actual crashlog, I don't really see much in there besides...possibly your custom browser source has something wrong with it. Maybe try disabling it and see if the crashes go away.