I'm on Act 3 currently of original campaign to Neverwinter Nights 2 and I haven't had any peasant growth in my keep since act 2. It's currently stuck at 23 peasants. My land security is considered high with the Greycloaks patrolling and I have no taxes on the peasants. Additionally I maxed out building my fortifications to increase my security. Could be this linked to me missing to recruit Orlen for my keep before Westharbor is destroyed? This has been bothering me for a few days and I wanted to know the solution to this problem.

I'm actually not sure. I've always recruited Orlen as I like filling out my strongholds in RPGs as much as possible, but under normal circumstances, peasant growth (along with Greycloak recruitment) goes up every time Keep progress advances. There are parts of the story where Keep progress comes to a stop in order to prevent you outpacing the story, so maybe check with Kana to see if that's the case. (Usually when Kana says you need to deal with some important story quest, that's a cue that Keep progress has stopped and won't proceed until you do the quest.)

That said, 23 peasants seems VERY low for Act 3. IIRC, I had just over 100 by the time I was ready to start the final part of the arc. What are some of your other Keep stats like morale and such?