This is a very complicated regiment. The first battalion consisted of recruits from Sachsen-Weimar-Eisenach while the second battalion had contingents (and different uniforms too) from
-Sachsen-Gotha-Altenburg (2 coys for a total of 312 men)
-Sachsen-Coburg-Meiningen (1 coy for a total of 104 men)
-Sachsen-Coburg-Saalfeld (1 coy for a total of 84 men)
-Sachsen-Hildburghausen (1 coy for a total of 114 men)
The first battalion, as you can see, wore the same uniform and there was probably a grenadier company that wore a similar uniform but with the addition of a mitre. But the second battalion (4th picture) wore 3 different uniforms and this is quite strange to see within the same unit. Plus the flags are only a guess as there appears that none are still extant.