Usage of Primary and Foreign keys in an EER diagram

Question

In my db I have three tables (I have more but for case is equal, users can be companies or single people).

• Users has a primary key id_user;
• Company has a primary key id_company and a foreign key users_id_user;
• job_offers has a primary key id_job_offers and two foreign keys: company_id_company and company_users_id_user.

My questions are:

1. Does a primary key make sense in job_offers? I don't think that there is a reason for it.
2. job_offers has two foreign keys, one related to company and other to users. Is there a problem with this? Does there exist another way to accomplish the same task?