Will damiyo typically only have samurai families from their Clan serving them, or will they more often have members of some other Clans serving them?

IE how strange would it be for a member of the Matsu family to be sworn to a Crab damiyo?

I think this would be quite unusual. Generally lords will have samurai of their own family serving them. Clan and family loyalties being very strong. Also every samurai has a lord so you would have to ask why he is no longer serving them so that he can serve another clans lord.

There are instances when it can happen though. Especially for player characters. Samurai will go to the wall to assist the crab sometimes. The Scorpion offered to send an army in support and the crab seem to be overly demanding when it comes to control over troops from other samurai stationed in the wall. So I guess that is a possibility.

Or if the players became emerald yoriki or magistrates. They would now be serving the emerald champion or another emerald magistrate directly.

If they became Ronin and then swore to another lord. But then they had better have a pretty good reason the new lord would want to employ a Ronin.

38 minutes ago, wastevens said:

Will damiyo typically only have samurai families from their Clan serving them, or will they more often have members of some other Clans serving them?

IE how strange would it be for a member of the Matsu family to be sworn to a Crab damiyo?

Through wedding, it isn't that unusual. But the other ways are more rare.

There was the hostage situation, where rival clans exchanged individuals to prevent attacks from their enemies.

It's not uncommon to find a courtier from a different clan at a daimyo's court. Said courtier is going to be a permanent resident and a perfectly sensible PC, but isn't technically one of the daimyo's 'subjects' - they're subject to the daimyo's law (because they live on their lands) and will probably aid and assist where it's in their clan's mutual interests (or at least not actively against them) but aren't the daimyo's vassal.

That said, yes, you do get people swearing fealty to out-of-clan lords without being Ronin at any point. In fact, one of the first adventures published for 5th edition, Wedding at Kyotei Castle, features one: Nasu no Shiba Shizuma.

"Nasu no Shiba Shizuma is Lord Takashi’s general and chief advisor. As a man well past retirement age, he also served the late Tsume Retsu in the same role. Decades ago, after Tsume Retsu came to the assistance of the besieged Phoenix clan at Nikesake Castle, Nasu no Shiba Shizuma swore his fealty to Retsu and was given permission by his lord to become Retsu’s yojimbo, to help unite the Phoenix and Crane in the valley against the Damasu no Akodo family. Though he still honors the Phoenix Clan and still bears the Nasu no Shiba name, he has served the Crane Clan for decades and is as much a Crane as he is a Phoenix."

8 hours ago, wastevens said:

Will damiyo typically only have samurai families from their Clan serving them, or will they more often have members of some other Clans serving them?

IE how strange would it be for a member of the Matsu family to be sworn to a Crab damiyo?

Rokugani "families" are clan by any sane definition so if you go by that metric pretty common. I expect that in any marriage each spouse also brings in a small retinue to their new clan as attendants. Over the years you can expect any single"family name" to pop out in other clans just from that alone.

So, uncommon, but not necessarily strange.