Yes you can claim anyone as a dependent if there living under your roof.
Yes, you can claim a qualifying dependent.
No
You may never claim your spouse as a dependent. You may, however, claim a standard exemption for your spouse if she does not have to file and you are not filing jointly (and as long as no one else is claiming her as a dependent).
If the "dependent" brother is under 19 and is not a full time student then you can not claim him as a dependent and you can not claim Head of Household status. How old is this brother?
I would yes
You can claim them if you provided for the person the year you want to claim him or her.
If they aren't a qualified child or a qualified relative, as defined, you can't claim them.
No, you cannot claim single head of household unless someone you claim as a dependent lives in your home.
No
No, sorry. You can only claim someone related to you as a dependent.
No, medical expenses for a dependent can only be claimed by the person who is claiming him or her as a dependent.
You are not eligible to claim yourself as a dependent on your federal taxes -- ever. However, you are allowed to claim a personal exemption for yourself if and only if no one else can claim you as a dependent, whether or not they actually claim you.