This last wave of releases has been rather unique with the release of two sets of very different Ronin models. The first set is the Blood Brothers and their servant. They committed some terrible crime on the mainland and have fled to the Jwar Isles. Pursuing them are the Sworn Sisters, who are honour bound to hunt down the Blood Brothers and bring them to justice.
The two sets play very differently to each other and tend to avoid working for the same factions, with the exception of the Ito Clan and the Silvermoon Trade Syndicate - those factions have access to both the Blood Brothers and Sworn Sisters.
There is a very specific technique to how the Blood Brothers start the game. At some point on turn 1, Ying-Jian will end up in base-to-base with Baichi and use "Saihai" to get the Blood Brothers moving up the table. The only time this might not happen is if the scenario is a VIM scenario and the Blood Brothers player feels they can be greedy on turn 1 - it's still a bad play in my opinion though.
After that the Blood Brothers occupy part of the board and form something of an immovable object - they function as MS3, Tireless models with Indomitable (1), so trying to drop their dice pools down requires some serious effort.
The main drawback of the Blood Brothers is their lack of activations - their other drawback is how much they don't like getting shot by ranged attacks. They're perfectly happy allowing your opponent to flail away at them, but getting the Blood Brothers to actually do things is quite hard. You need to build a warband with plenty of models that can do scenario actions and function without support to compensate for the amount of Rice the Blood Brothers eat up. The factions that do this best are the Jung Pirates and the Silvermoon Trade Syndicate as they both have MS3 profiles that start at a cheap 4 Rice - Kyoaku-Han and Kohanin. This means you can fill up the warband and still have rice left over for a utility special card or two.
Of the factions that can use the Blood Brothers, the Ito Clan and the Savage Wave probably have the hardest time. For the Savage Wave it's a problem with filling the rest of the warband with profiles that could function away from the Blood Brothers. For the Ito Clan it's more of a play style problem; the Ito Clan typically has a smaller warband than the current meta and relies on being incredibly aggressive to reduce the opposing warband's model count. Being that aggressive is hard work with the Blood Brothers.
In conclusion, use the Blood Brothers to take and hold part of the board, once they're in position they're incredibly hard to shift as long as none of them get shot. Don't expect them to do scenario actions unless there is literally nothing else for them to do. Finally, once one falls, things go downhill in a real hurry.
More versatile than the Blood Brothers, the Sworn Sisters are similar in that they work together, but the similarity ends quickly as they don't lose out on function if you don't feel like taking the full trio. I can see several factions just taking Yanjing for her incredibly powerful ranged attack.
The Sworn Sisters were designed to present their player with a plethora of options every turn, and succeed at that design goal with style. You can setup some very chess-like traps by leaving one "exposed" and then utilising Bodyguard or Sister's Succour to force your opponent into fighting the Sworn Sister of your choice. Or you can use Command to bring out full on aggression and take the fight to your opponent. Or you can use the Sworn Sisters Ki feat and play the activation game. Don't be fooled by their MS3 stat either, they tend to sit at MS4 in reality as long as at least two of the Sworn Sisters is still on the board. The skill ceiling for the Sworn Sisters is incredibly high, so expect to continually be caught out by them fairly often.
With the changes to the Golden Sentinels - they are now ludicrously good value at 8 Rice - and Yukio Koshimori, you can now build warbands made up entirely by Imperial models. It's certainly powerful, and the Silvermoon Trade Syndicate probably works best with them due to the variety of their special cards, but the Ito Clan also does extremely well if you swap a Golden Sentinel for an Ancestor Spirit to help fuel Yukio and the Sworn Sisters. Control Imperial Ito is actually a thing, you have been warned.