One useful thing to do at this point is to ask yourself the following questions:
- What these machines are doing on your network[who put them there, what are they doing with them?]
- What services they need to access [internet? network shares? bespoke accounting intranet app?]
- What level of service you are required to provide to these machines [Which has a bearing on whether or not you need department admin account access, for example]
Simply asking yourself these questions, if you haven't already, will improve your thinking about the problem, and posting your thoughts on them here will improve the answers you get from us. At the moment your question does read a bit like these things fell through an open window and landed on your desk at random and now you're wondering what to do with them...
I have no clue as to what they run, if they have an Anti Virus installed (I heard all about the: Mac's don't have viruses)
Macs don't come with AV installed by default. I would address this - regardless of the debate about mac viruses (and you will indeed find people who will believe macs are "hacker proof" out there) you don't want these systems holding files that might infect other machines on your network.
some of them (2) even connect to my network using the wifi of the 3rd one, which doesn't even give them our intranet IP.
That's nothing to do with "running macs on a windows network". That's basic configuration of the wireless connection on those machines. You presumably have a wireless infrastructure already? What happens when you connect those clients to the normal wireless connection?
What should the procedure of having Mac's in a windows network?
The answer to this depends on what you're hoping to achieve with them.
What we do: Join them to the Windows domain (see this question on our sister site for Apple issues), have people log in using domain accounts, not local ones.
I know I can't have an admin account on them.
I don't see why not, we have local and domain admin accounts on all of ours.
Should I give them a seperate subnet?
Why? What would you hope to achieve by doing this?
Any tool like spiceworks that I can see their configurations? installed apps? running services?
Spiceworks will work, via SSH, as Lucas says.