2. The amount of the companies' capital is limited by the authorized shares.
[I assume you are talking about more than one company. In that case, the possessive apostrophe ( ' ) goes AFTER the last 's'.
4. A member death has no effect on the company.
One last suggestion:
3. A company is a separate legal entity and therefore has to pay corporation taxes on their profits. [This is opinion. The sentence is not wrong, basically. This just sounds better to a native English speaker]