Caveat: you are allowed to hotspot your phone.
Hotspot the two wireless computers direct to your phone.
Buy a couple of el-cheepo wireless adapters (go into the USB) for each wired computer, like these:
https://www.ple.com.au/Products/6194...B-Nano-Adapter
May even be cheaper than having to get a sim card for the 3g router andytug mentions.