Very easy. Leave most of your party where you entered the tower area. use stealth of some kind, thief, potion or spell to get to the tower. Go upstairs, pick up any valuables that you want including the tome. It doesn't matter if you get charmed as there is nobody else in your party to clobber you or vice versa though the potion that you get upstairs at Candlekeep makes you resilient to it. Alternatively use potions of perception, dexterity and master thieving. Use stealth to get back out. There is a potion of oil of speed in there which helps get you out without having to keep on trying to hide.
You need to use a bit of lateral thinking if you want to go where Love Pride etc. are. However that is not needed to get the Tome. I usually go to the tower at level 1 and come out as level 5. To do that you need a small party.
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