I included relevant background to illustrate how convoluted the system can become, skip to the bottom if you just want to see the question.
I've gone off the deep end and broke everything by making a homebrew spell system that completely replaced the pathfinder system. Magic was initially destroyed in a cataclysm per my lore, and now everybody can use it as it is gaining more prevalence, though obviously melee classes will implement it differently than ranged.
It is based around a system of magic words that are combined to generate a desired effect: "burn" + an amplifier, ex: "three" results in an above average burning effect. These words can be chained together to create some pretty neat spells, and I've been kept on my toes by some players trying to abuse the literal wording of spells to teleport between planes using a conjuration ritual. The limiting factor is mana, both in terms of a maximum capacity that each player can use each day and in terms of per-round bandwidth. This means a player can only output X mana each round, so they must channel for more rounds if they want to use more modifying words, and have a hard cap on how much they can cast without resting. Additionally, they can make rituals, which effectively store magic over many days to power an exceedingly powerful spell, and can enchant items that automatically absorb mana, allowing X casts of a spell per day for free.
Players are able to learn the words as they are playing, and write combinations of these words down in physical spellbooks. To help facilitate this, I have 'black pages' that contain a 'spell' already written out (they obviously may or may not know what it does depending on what words they know) along with a single magic word and its definition in common. They insert these into their physical spell-books. I find that my players are much more engaged when they have to physically flip through a book, and it helps avoid those 'quickly googling the wiki' moments. Besides this, there is a real world analogue to preparing spells each week, since they must literally construct their spells and write them down for easy access during play, though the smartest players in my games have started memorizing words directly and making free-form spells mid combat, which I find to be a very cool way of showing both that they and their characters have grown.
These players are at a severe advantage because if they are able to overhear enemies casting, they are able to use a particular class of spells to counteract the effects as an interrupting action, assuming they know the words well enough to instantly cast the dispel.
That said, half of my old group dropped. Luckily one of my friends has three buddies who are interested in joining up with experience in RPGs ranging from none to fairly experienced with recent DnD rulesets. The remaining half of my party is used to the new system and highly engaged in it, but I'm concerned that the newbies will be put off or confused by the system, and I unfortunately don't have time to do a multi-hour walk-through at this point.
So, how do I ease the new players into my convoluted homebrew system without neutering the fun of the rest of the party?