It can be many things. You are unlikely to have a trojan on macOS, but you use parallels, and I dont know how it is done so it may eventually have a windows nastiness of some sort.
When it is very slow, try to connect to the same site with your husband machine and compare. This way you will know if it comes from the site or network capacity or if there is some problem with your own machine.
Also have a look at your livebox : if its seems to have a frantic activity when you are not doing anything network related, that is bad news, you may have something running you dont want to.
I think a trojan will show also on monitor activity (little black and green icon) and ressources use but with parallels, I dont really know how it works.