So you're a Frugal Mage Warrior, and you've decided to share your collection with your playgroup. Things seemed to be going well, until you guys started building your spellbooks.
You argue over cards, and don't want to tell each other what cards are unavailable because those cards are in your book and you don't want your opponents to know that. While it's possible for many casual players to get along just fine in this situation, ultimately it means that you know always know what's in your opponent's spellbook and it can be less balanced that way for reasons that have been discussed elsewhere.
But it doesn't have to be like that. It is possible to share your collection fairly. Let's solve this problem step by step:
There are two main problems with sharing your collection:
1. Your opponents know what cards you're using ahead of time and vice versa.
2. Fighting over cards
The most obvious solution to both of these that jumps out at me is to split the card pool into smaller parts and rotate them between players every so often. Of course, that runs into the problem of "what if X wants to play a warlord against Y who wants to play a Forcemaster?" That makes it sound like we'd have to make our own custom "sets" from the cards we have. Furthermore, if you only have three sets for a playgroup of four or five people that can make things even worse. You could also try having people pair into teams each month and have them cooperate with their partner to build their spellbook. For instance, a forcemaster player would be partnered up with a warlord for a month, and they would take turns with the cards they need for their spellbooks using a smaller cardpool shared between the two of them, i.e. FvW, FiF and Core. Or you could just require all new additions to your playgroup past a certain point to have a core spell tome 1 and/or 2.
I recommend dividing everyone in your playgroup up into teams of 2 players each month, and assign each team a cardpool consisting of four small expansions or an equivalent thereof, where
1 Big Expansion=2 small expansions
Arena Core set=3 small expansions
Battlegrounds: Domination= 1 small expansion
Academy Core set=1 small expansion
This is two small expansions per person on average. If you have one of every set that currently exists in the game as of December 2nd, 2015, then you have about the equivalent of 13 small expansions. So if you leave out one small expansion each month, then you can support six teams of two plus one extra person who can rotate in and out of teams.
With only 1 Core set, 1 big expansion and 1 small expansion, you have the equivalent of 6 small expansions, and you can split the card pool into the core set on the one hand and the expansions on the other. However, you might need to split the main core set into three core spell tomes and rearrange the card pools, depending on how balanced this is.
Also, some cardpools might not be balanced with each other. Make sure to assign cardpools fairly.
Autoincludes and their alternatives and counters
Core: teleport, dispel, dissolve
Battelgrounds Domination: astral anchor, cascading forcewave
Forged in Fire: disarm, rust
Academy: arcane ward, crumble, disperse
Druid vs Necromancer: acid ball, corrosive orchid
Conquest of Kumanjaro has Wizard Tower.
Academy has arcane ward, Conquest of Kumanjaro has Enchanter's Wardstones, Domination has reinforce and Auto Kronig, Forged in Fire has Conquer and Wall of Earth, Druid vs Necromancer has Cloak of Shadows, and Blur will be released in a future expansion.
If any opponents both 1. do not have teleport or wizard tower in their card pools and 2. don't have sufficient counters to teleport and wizard tower in their card pools, then feel free to house rule those cards.
As for those who want to play a forcemaster against a warlord, or a druid against a necromancer, you're probably going to need to make some custom card pools for each player. However, that could take a bit of experimenting and feeling out the playstyles of your playgroup until you get it right.