Check what network and speed the devices are actually using. If old they may have been set up to work with an elderly router limited to one of the original Wifi protocols, which are slow and use the overcrowded 2.4GHz band. All devices should elect to use one of the newer protocols, and switch to a less cluttered band or channel while they're at it.
Chaps used to the slow pace of development of mechanical gizmos may be surprised at how quickly electronics are moving. A 5 year old smart phone is out of date, not because it's badly made, but because its technology continued to develop rapidly after it was built. Wifi is a good example. The first implementation of 801.11 appeared in 1997 and ran at 20mb/s in the 2.4GHz band. Just over 10 years later 801.11n delivered up to 300mb/s at 5Ghz. New computers and phones now come with 801.11ac (first available 2014), and might get 1300mb/s at 5GHz. A very new computer might support 801.11ad, and 802.11ax, 802.11ay, and 802.11az are in the pipeline.
Whether these speeds are actually achieved depends on how electrically noisy the location is, and how thick the walls are. Looking at slow Wifo connections with a traffic analyser and sniffer often reveals loud competition from neighbouring networks on the same channel, and man-shouting-in-noisy bar conversations like:
iphone to router – connect me to internet please
router to iphone – what? Say again.
iphone to router – what? Say again
router to iphone – OK, I said say again
iphone to router – connect me to internet
Router to iphone – OK, use this address
iphone to router – what? Say again
etc etc. The link spends more time asking for repeats than transferring information.
I'd have thought 18mbs would be fast enough for most simple purposes. If it's not easy to fix I'd tolerate the problem and be pleasantly surprised by the improvement when those past-it Apple devices are replaced in due course!
Dave