Welcome to APUG.
The Ica Sirene is a bottom of the range camera as it has a 2 element Helios lens in what looks to be a self cocking shutter, plate holders are quite easy to find but see the sticky thread here about the types of fit. Film adapters were made but are slightly more difficult. It's a very simple two blade shutter so may well appear loose.
I've put new focus screens in all my cameras of this type but they often need quite thin glass (1.5mm) which is more prone to break.
The other camera lppks interesting.