Well, since you're asking I'll share a few thoughts.
First, you don't technically NEED to install cf in each server--if by that you mean for the two clustered iis servers to each have their own cf. You COULD have cf on only ONE server, talked to from BOTH iis servers. That would be a rare setup, BUT it's possible, yes. It's a variation of another notion (also not used that often): the connection of a web server machine to a cf instance running on a machine WITHOUT that web server is what's been traditionally called "distributed cf". There's no button or ui to "make that happen". Instead, there are steps in the cf docs.
But I don't think this is necessarily the best way to go. As you've already licensed the two cf servers, you can and probably should just stick with CF on each machine. There's benefit to redundancy and flexibility in being to take one down while the other remains running.
What I MIGHT question is whether you should bother with the registering of remote instances as you've done, which presumes you'd be using cf enterprise's clustering feature. As you already have iis clustering, you don't NEED the load balancing aspect of cf clustering.
The other major part of cf's clustering feature is session replication--and some using cf clustering choose not to enable that for various reasons. In that case, you'd REALLY not NEED to use the cf clustering feature.
And some folks who use that Cf session replication feature don't even need that, as cf2016 introduced redis session storage, which can be shared between multiple instances. (Note also that Cf redis sessions does not require use of cf Enterprise.)
It's true that Cf session replication REQUIRES use of the cf admin j2ee sessions feature, while cf redis sessions instead requires those be DISABLED. And some folks fear that Cf j2ee sessions "aren't as secure" as traditional cf sessions, but that's only true regarding their default configuration. Cf sessions can be made as secure as j2ee sessions.
Finally, I realize clustering is only in cf Enterprise (not Standard)--and without it, you may think "did we waste money then on cf Enterprise?" But there are MANY more features cf Enterprise offers beyond this, and I've done an entire talk on the topic, available (recording and pdf) at carehart.org/presentations.
If somehow I didn't address your last comment seeking thoughts on your situation and any tips, let us know what you may still be seeking to confirm/check.
/Charlie (troubleshooter, carehart. org)