They once occupied a territory from the edge of the Czech Republic and Poland as far north as Berlin along the Spree River, but they have been assimilated by the Germans over much of their historic territory. Here is the location of Lusatia. As you can see, it is split between Saxony and Brandenburg.
Here is a closer view of Lusatia. All of the municipalities in this area have names in both German and Sorbian.
The four generations shown in the initital photograph are wearing the Lower Sorbian Costume from the area of the city of Borkow [Burg]. This is worn in one version or another throughout the region of Chóśebuz (Cottbus), The headdress is meant to look like one very large scarf tied in a knot, but its largest iteration is actually made of three separate pieces pinned together. In the everyday costume it is much smaller, and is actually made of one large scarf. This is the best known of the Sorbian costumes.
An overview of the costumes of this region is made more difficult by the fact that each local tradition may have a work costume, everyday costume, going out costume, church costume, dance costume, bridal party costume, etc. There are generally considered to be 11 costume regions. I will name each region first in Sorbian, and then in German. These are all shown on this map above. We will travel roughly north to south.
1. Nowa Niwa (Neu Zauche)
2. Lubnjow ( Lübbenau)
3. Chóśebuz (Cottbus)
Video of a street dance in the town of Hus (Maust), to the northeast of Chóśebuz (Cottbus). The girls have dressed up in the costume but not bothered to put the headdress on.
I give you the Annemarie polka.
Video of a dance performance from this region by the Sorbian National Ensemble.
4. Zły Komorow (Senftenberg) & Grodk (Spremberg)
5. Mužakow (Muskau)
6. Slepo (Schleife)
Video of a folk song from this region 'Daj mi Jadno Jajko'
7. Wojerecy (Hoyerswerda)
9. Klětno (Klitten)
10 Budyšin (Bautzen)
This costume and the following one have overlapping regions, this costume is found in the southern and eastern parts and is only worn by Protestants.
11. Kamjenc (Kamenz) & Radwor (Radibor)
This costume is found in the northern and western areas and is only worn by Catholics.
Smjerdźaca, I assume, doing a dance called Hanka.
Here is a website which shows some of the variation of the Lower Sorbian costume. The website is in German.
Here is a link to some videos of the performances of the Sorbian National Ensemble.
Lotar Balke & Albrecht Lange, 'Sorbisches Trachtenbuch', Bautzen, 1985
Měrćin Nowak & Pawoł Nedo, 'Serbske narodne drastwy 1.zwězk - Drasta Slepjanskich Serbow', Budyšyn, 1954
Jan Meškank, 'Serbske narodne drastwy 2.zwězk - Drasta Katolickich Serbow', Budyšyn, 1957
Měrćin Nowak-Njechorński &Lotaŕ Balko, 'Serbske narodne drastwy 4.zwězk - Drastwa Serbow wokoło Chośebuza', Budyšyn, 1964,1991
Błažij Nawka, 'Serbske narodne drastwy 5a.zwiazk - Drasta Serbow Wokoło Wochoz',
Gerat Apelt & Albrecht Langa, 'Serbske narodne drastwy 5b.zwjazk - Drasta Serbow Wokoło
Klětnoho', Budyšin, 1979
Błažij Nawka 'Serbske narodne drastwy 6.zwiazk - Drasta Evangelskich Serbow Budyskeho Kraja', Budyšin, 1979
Lotar Balko, ' Sorbische Stickereien', Bautzen, 1976
Rolf Langematz & Pawoł Nedo (Paul Nedo), 'Sorbische Volkskunst', Bautzen 1968