If the SF354 are the drive belt models (which if they are single sided is highly likely),the belt has probably long since disintergrated. Would probably be worth opening them up and seeing if it has (you may find nothing but black gunk). In which case you may well have three faulty drives. If so they can be repaired easily with a new drive belt. As they have their own power supply they are unlikely to be effected if your STs is a bit weak, unless theirs is also on the way out. The internal drive on the STFM is more difficult to diagnose. On some models some capacitors fail stopping the drive from spinning, or if it is a real early drive (the very early STFMs did ship with single sided drives) then you may well have the same issue as the 354s. Or it might well be, as juansolo suggested, gunk on the floppy drive head. You can buy a floppy disk cleaning kit (or clean it yourself with a q-tip and some isopropyl. Another thing to note is that if the language disk is on a double sided disk, the 354s won't be able to read them as they are single sided only. Which may mean that only the STFM drive is caput.
With the floppy disks, I have actually found them to be a lot tougher than most people say.. provided they have been kept dry. A lot of so called 'dead' disks can be brought back to life if you gently clean them with isopropyl and a q-tip. Most of my floppies are still going strong in a 800 plus game collection and I still have a lot of random software disks that are also fine. They are all now stored in sealable plastic bags now to add to the protection. In my experience a properly cared for floppy disk will retain data for longer than a CD-R, which seem to spotaneously self destruct after about 10 years, regardless of how they are stored. I had one CDR turn to what appeared to be liquid inside itself, you could tip the CD and watch it run about.
In answer to your actual question though.. no it will not matter if you use a DSDD floppy, or even a DSHD one if you cover the HD select slot on the disk, though you won't be able to use HD disks at full capacity without more hardware mods, and they are allegedly less reliable formatted this way (not done this myself). I know there were 'single sided' floppies when the ST first came out, but they died out pretty quick. You can just format the DSDD disk as single sided if necessary. The best way to test the drives is to try and format a floppy. If it completes a format of both sides you are probably fine. If it only manages one side and none of the other then it is probably single sided. If it only partially formats either one, the heads need cleaning.