Live in Bahrain and work in Saudi Arabia

Hello!

I am helping someone from Portugal who should be working in Saudi Arabia and will be living in Bahrain (travel everyday by car). I have been doing some research but I still have some doubts:

- If this person has an employment contract in SA he should easily get a work visa there. He can also apply for this multiple entry exit visa in SA if I understood correctly;

- when travelling daily to Bahrain, what kind of document has to be obtained there? I understand there is this CPR - but for that a residency visa in Bahrain is also necessary right? and in that case, isn't it necessary to have a sponsor there? what if the person does not have a sponsor in Bahrain but only in saudi arabia?

Thanks for your help!