You should recuse yourself. Any attempt to influence the career development of someone who is related to you, or with whom you have a close personal relationship, could lead to a conflict of interest or the appearance of a conflict of interest and should be avoided. This also applies to performance evaluations of personnel who are related to you or with whom you have close relationships.
You may not be part of a situation which leads to a conflict of interest or the appearance of a conflict of interest. In your case, if your investment in a large company is so small that it will not be affected by the outcome of the procurement process, you should be able to continue to participate in it. If you are in doubt regarding these matters, discuss them with your hierarchy or verify with the Finance and Procurement Department or Internal Audit.
Yes, as long as you do nothing to influence CERN’s decision to retain the services of your brother’s company. You should inform the respective CERN officer of your relationship and clarify that your input should not be seen as interference in CERN’s decision-making process
No. You should not do anything that could influence, or could be perceived as influencing, the decision-making process, because you have a conflict of interest.