It's clear that you're enthusiastic about lifting which is really good, but--and I mean no offense by this-- based on what you have said you are also probably not knowledgeable enough to make changes to the routine.
The front squat is significantly different from the back squat, and the entire program is built around the core lifts so not doing back squats makes a big difference. What is it about the low bar squat that you are having trouble with? The difference between high bar and low bar is relatively minor at a beginners level so you could do high bar until you can find someone to show you how to do low bar or you watch enough videos on it or whatever you need to do to feel comfortable.
For lunges, you can shorten your stride to put more emphasis on the quads, but this puts unnecessary stress on the knees for reasons very similar to why when you squat you need to at least go to parallel. The whole point of lunges is to work your glutes. I know you probably want massive quads for their aesthetics, but you need to build up your hamstrings and glutes as well or you risk destroying your knees.
You're also probably doing too much assistance work, but I would need more info to make that assessment. Suffice it to say that RDLs, or any form of deadlift really, is very taxing on your central nervous system.
