Family Matters - Velen
This quest begins immediately following the completion of Ciri's Story: The King of the Wolves, one of the main story quests in Velen. Additionally, the Ciri's Room side quest is added to your quest log at the same time as this one and it's recommended you do it before leaving Crow's Perch.
Below are a list of all the things you will have to investigate inside of the room the Baron lets you investigate. Above you can find the compass location of everything mentioned below, use your Witcher Senses and you'll probably be able to find it all yourself.
1. Off Color Wall
2. Painting (and hole behind it)
3. Candlestick inside wardrobe
4. Flowers & Knicks on the wall
5. Broken Wine Bottle & Scent
Once you've located all five things follow the scent of the wine out of the room and to the Talisman which you'll find under the floorboard on the stair's landing. The quest will update at this point and you can speak to the Baron if you want - or you can search the other room across from Baron to learn more about Tamara.
If you decide to search the second room, use my screenshot below and list to make sure you've found all there is to find. Note: While you have access to both of these rooms you can loot everything in them without alerting any guards and without any repercussions.
1. Ugly Doll
2. Incense & Old Key
3. Letter to Tamara
After investigating the wardrobe with Incense you'll have a new smell to follow. It leads you into the basement and to a locked door which the Old Key will open. There will be an Altar of Fire in the room for you to investigate and a letter which you'll want to grab. Once you've concluded with this part of the quest return to the Baron and speak with him to get another quest update. Now we're off to see the Pellar.
When you arrive at the pellar's house some of Baron's men will be there to greet you. Unless you killed Baron's Men at the Crossroads Inn you'll have a few choices available to you; if you killed them then Baron's men immediately attack you. The options that are available to you are shown in the screen shot above. 2 and 4 allow you to avoid conflict. From what I can tell, killing them doesn't change anything in the future except maybe a line or two of dialogue somewhere.
Speak to the Pellar to update the quest again and to receive the quest, A Princess in Distress. For this quest you'll have to rescue his goat, complete it then speak to the Pellar to update Family Matters. You'll learn about the Botchling and have to return to Baron and speak with him to update your quest again.
When you arrive back at Crow's Perch the stables will be on fire and you'll have the option of rescuing the stable hand and horses or letting them all burn. If you decide to rescue him you'll get a cutscene which transitions into you talking to the Baron, otherwise just talk to the Baron to advance the story forward.
If you decide to save the stable hand you'll have to take the ladder up to the 2F of the stables and use Aard to clear the rubble. I'd highly recommend you save him as there is a chest on the 2F of this building you can loot with new Crafting Recipes as well as some bonus EXP for saving him. (Plus it's the right thing to do and Geralt is a white knight after all!)
After saving the stable boy you'll have to fist fight the baron then there will be a long cutscene where Geralt gets his answers. The next part of this quest will branch off into two options, you can either kill the Botchling and find Baron's family by taking the blood to the Pellar and having him perform a ritual OR life the curse from the Botchling.
Lift The Curse: If you choose this option you'll have to protect the Baron as he carries the child back to the manor. Wraiths will attack you each time the baby struggles and you'll have to use Axii on the Botchling repeatedly otherwise it'll become enraged and you'll be forced to kill it, automatically picking option 2 for you.
Kill the Botchling: Defeat the Botchling and take its blood to the Pellar. You'll have to protect him during a ritual that will have Wraiths spawning to attack you. During this ritual you'll have to relight the fires a total of 3 times to complete it. To save time, interact with the braziers and use Igni that way instead of casting it. Interacting with the braizers doesn't cost Stamina. Be sure to walk the Pellar back to his house for an extra 100 EXP.
Regardless of the option you choose the quest will eventually lead you to the Fisherman's Hut just outside of Crow's Perch next (pictured below). If you decide to Lift he Botchling curse you'll have to do a little bit of detective work before finding your way here following the Lubberkin.
Speak to the people living inside the Fisherman's Hut to learn more about Tamara and Anna. When you're done the next update for your quest will have you return to the Baron and fill him in. If you've already been to Oxenfurt throughout your travels and met Tamara then you'll get a different response from the Baron when you visit and it will skip the objective of having to find Tamara.
When you arrive back in Crow's Perch, if you saved the stable boy before he'll stop you to speak before reaching Baron and give you some Crowns, the sergeant will stop you too but empty handed. When you speak to Baron you'll be thrown into a cutscene which will lead into the Ciri's Story: The Race quest.
On your way out of town after speaking to Baron the Pellar will give you the Forefather's Eve Quest - only if you've completed A Towerful of Mice Quest however. Last but not least the Baron himself will chase after you on your way out of town and give you another Ugly Doll that he has made.
(Optional) Your next stop is the town of Oxenfurt - which will be the first "actual" town you visit in Witcher 3. If you haven't been to this town before then you'll be able to get in using the paper the Baron gives you, or a fake transit pass you got earlier in the game. If all else fails you can always swin across the water to reach the town. All you have to do in this town is speak to Tamara to update the quest.
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Investigate all remaining leads in Velen and find the Baron's wife. - In order to progress this quest any further you'll need to complete Wandering in the Dark and Ladies of the Wood, both story quests in Velen. Completion of the Ladies of the Wood quest will update this task on Family Matters and tell you to return to Baron and speak with him. Also, depending on the actions you chose during these quests will determine what comes next in the story for you.
Speaking with the Baron will begin the next quest of Ciri's Tale, Ciri's Story: Out of the Shadows. All you need to do for this quest is defeat the basilisk then climb the tower for a scene. After this story quest you'll receive the quest Return to Crookback Bog which is a secondary quest for Geralt.