yes, they will be treated as seperate entities. if you have multiple companies, then each company can have its own adsense ID. also if you have just one compnay, then you can have one individual account and one compnay account as well
yes you are allowed, 2 companies imply 2 different tax numbers, 2 different bank accounts and 2 different emails used in the adsense register
I heard from joel comm before that you can have one individual account and another business account Is that right?
Yes it is allowed. the other account should be named in your Company's / Business Name. and check payment will be in the same company name. that is allowed!
You can have two adsense accounts. One using your name and the other your wife's name.Adsense for Search, contents, feeds and referrals earnings would be separated. Just make sure you won't have a divorce or something. She might run away with your earnings.