To simplify the work of this amazing mod, please allow me to do the research for historical references!

For the Russian uniform, these were the standard russian black fild marshal uniform, worn by Nicholas I, Alexander II, and partly Alex III and Nicky II, with the azure sash and star of the Order of st Andrew, the highest decoration of the Russian empire

1st Example[i.pinimg.com]
2nd Example[lh3.googleusercontent.com]
3rd Example, here worn by Franz Joseph I of Austria (IMO, the best example of the uniform, this specific version was used during the period around the 1850s and the 1880s)[upload.wikimedia.org]

Later, Russian Emperos tended to use this uniform, although they never really had a specific one, Nicholas II later in less formal events, and during all of WW1, switched to the very simple field uniforms for russian generals, with only the order of Saint George as a visible decoration:

Formal Uniform[europeanroyalhistory.wordpress.com]
Informal field uniform[scontent-mxp2-1.xx.fbcdn.net]
2nd example of the latter[pbs.twimg.com]

Instead, for the british, they mostly used the field marshall uniform (for kings):

1st example[i.pinimg.com]
they also used often navy admiral unifroms, such as this[i.pinimg.com]
For female (british) monarchs, who did not wear military uniforms, this was pretty much the way to go, with the blue order of the garter and its breast star[c8.alamy.com] you'd just have to adjust the dress to fit the historical period, this is victoria in the 1850s[upload.wikimedia.org]

A Small fix for legitimist france, which is complex since they never lived with official uniforms past the 1830s, so we don't have many examples apart from the very 1820s like Charles X with an hussar uniform and the sash and breast star of the order of the holy spirt for the later game past the july revolution, an idea would be that after the 1850s they'd switch to a more "standardized" unifrom, such as either the one of Napoleon III (But with the correct sash and medals) or like in this painting of Henri V, the legitimist pretender

Example[i.ytimg.com]

Otherwise, the unifrom for the legitimists I'd suggest the most, is the army uniform that Charles X and his son Louis XIX wore:

Example 1[upload.wikimedia.org]
Example 2[www.instagram.com]


I hope all of this helped and that one day i may see these in the mod! Godspeed and thank you for the great work!