MISRA is a C/C++ coding standard that your software should adhere to.
It's not compulsory, but highly recommended. It is meant to reduce the
risk of erroneous behaviour by faulty software.
The ISO-26262 defines standards and procedures regarding product safety,
that you need to follow for the complete development of your product,
mechanics, hardware and software. The ASIL level is related to the risk
that a malfunctioning system poses upon the user. E.g. the
airconditioning in the will typically have a relatively low risk level
(ASIL-A or QM ("meaning "no risk")), whereas something related to the
brakes will definitely have a high risk level: ASIL-D.
Whether you can use a certain processor or compiler all depends on the
complete system. It is possible to develop an ASIL-D (highest risk
level) with an Arduino or two, if you really want to; but then you'll
need to put an enormous amount of effort into implementing all the
required safety machanisms. Without knowing anything about your product
except that it is "brakes related", it is impossible to tell.
Considering all that, I would strongly suggest that you get support from
an established automotive supplier, instead of looking on a hobby-ist
forum like this one.
Send me an PM if you'd like to know more. I am an freelance embedded
systems professional and been developing safety related products for the
automotive industry for several years.