As far as the books go, the 4 that are part of Amren's quest cannot be gained without Amren in the party. Without Amren you can't gain access to the underground shrines where the books are located.
Now, for Lenali's Sorrow. There's a specific chain that needs to be followed:
Lenali gives you a doll that you need to take to an Elf elsewhere in Eirulan, on the Terrace of the Falls. In return, you'll get a flask of Elven ale.
Take the Elven ale to the Azunite Desert outpost. There's a soldier there who will take it in exchange for some Skath Cat ribs.
Take the ribs back to Eirulan and talk to a soldier in one of the upstairs rooms at the inn. He'll give you a lucky statuette of Xeria. These steps can all be done within Act I.
Take the statuette of Xeria to Snowbrook Haven, and give it to a soldier in the dining room. He'll offer you a Morden head on a pike.
Take this rather gruesome trophy to Aman'lu. There's an Elf there who wants this kind of thing, and he'll give you a flask of sacred water. This is far as you can go in Act II.
Take the water to the Northern Plain of Tears and hunt around for an elevator that leads down into some underground ruins. Down there, you'll find a prospector who's running low on supplies. Give him the water, and he'll give you a supposedly priceless Agallan relic.
Up on the northern wall of Kalrathia, you'll find a Half-Giant who's a bit depressed and wants something interesting to study. Give him the relic, and he'll give you some Harpy feathers.
Take the feathers back to Aman'lu, and talk to the local fletcher. She'll gladly take the feathers, and give you what you've been looking for all this time - the Aman'lu Orchid.
Take the orchid back to Lenali in Eirulan, and claim your reward. The quest log says the suggested level is 3, but considering it takes you until Act III to complete, this is probably the most annoying quest in the entire log.
From cradle to coffin... Shall my wickedness... Be your passion