Allocate out your memory to your individual VMs leaving at least 2 GB for your host OS. This means for Server1 above you could probably have 20 to 22 virtual machines given the specifications you are giving. HOWEVER, there are many other limiting factors here, such as storage throughput, network throughput, and intended usage. Here's the other thing, too. Windows Server 2008 R2 can run with just 1 GB vRAM and 1 vCore, but that's pretty much at idle. If you have anything running or demand on it, it's probably going to want more memory than that allocated. I don't know the software, demand, environment etc. that you are working with. At most of our small business offices with five to ten computers, their domain controllers running Server 2012 want between 1 GB and 2 GB of vRAM even with very little usage and only performing DNS/Domain services.
There are so many other factors besides just CPU and memory that go into ensuring you have acceptable performance for your virtual machines. The two most often overlooked are storage throughput and network throughput. If you are trying to run 20 virtual machines through a single gigabit ethernet port you will have some severe network congestion for any services trying to access those servers. Likewise the hard drive throughput is going to greatly impact the speed of all virtual machines.
Again, I don't know the exact specifications of your business environment or needs, the demands you are going to be facing, software utilized, etc. However, I would probably say that around eight to ten virtual machines on the Server 1 would still remain pretty efficient. With improved hard drive throughput and multiple NICs you should be able to push that a little higher, but it seems that is your limiting possible factor right now. As for Server2, you have plenty of memory, but you have very limited total storage capacity, even though it is faster SSD storage for improved throughput. Additionally the processor doesn't have a whole lot of multithreading capabilities, but the E3 1225 can still be a pretty decent performer. I'd probably suggest about five to eight virtual machines on Server 2 but that's really going to be pushing the network, storage capacity, and processing capabilities of that server pretty noticeably.
Hopefully this gives you a bit of a benchmark to look at, but unfortunately it's just a rough estimate.