Attribution of paintings
 

IMHO, The portrait n. 133 Margareth Douglas could be by Daniel Mytens.
The portrait n. 135 Lady Arabella Stuart coul be by Marcus Gheeraerts.
Regarding Mary, queen of Scots, The portrait shown is, yes, by anonimous
but is in National gallery of Scotland.
The painting in NPG is after Nicholas Hilliard and is different an only half figure