The bow brooch worn during the French State visit in 1950 is a ruby and diamond bow brooch. It was later worn by Princess Margaret. As far as I know, it was not among the jewels sold at auction after Princess Margaret's death, so I guess it must still be with Lord Linley or Lady Sarah Chatto - unless it was a loan from the Queen to Princess Margaret and that the jewel reverted back to the Queen after her sister's death. It could possibly be a Greville jewel, but I have no indication proving this.
The large diamond bow brooch worn in 1961 by the Queen Mother is definitely a Greville jewel. The information was disclosed by Hugh Roberts in The Queen's Diamonds. According to Roberts (page 238), the brooch was made by Boucheron (as proved by the box in which it is kept, with the stamp "Boucheron") in 1900 and resulted from the dismantling of a knot-pattern diadem. It was originally partly articulated to allow adjustment of the bow.
It is a beautiful brooch, I would love to see it worn again!