Hi space,
This thread really belongs in the Windows8 network forum, especially since you have a server involved. Speaking of which, what server software are you running?
In any case, you have several things going on, but it appears that you have some confusion between domain logins on your W7 & W8.1 computers and a local network printer resource. The real question is have you setup W7 Homegroups to accomplish this printing on both computers, or are you relying on server resources to manage your print queues? If you haven't used Homegroups, you are really shooting yourself in the foot as you are relying on server based printing resources which are infinitely more difficult to manage.
I would suggest that if you haven't already created local or non-domain logins on the W7 & W8.1 computers, that you do so. I'd also physically disconnect your server connection to your home router (either turn off it's wifi adapter or disconnect it's Ethernet cable) as well as turn off the server altogether. Unplug it's power cord for now to make doubly sure it's not broadcasting on your LAN. Then on the W7 computer, create a Homegroup, which makes your W7 machine the Master in the homegroup, and then use that Homegroup code over on the W8.1 computer and add that computer to the existing W7 homegroup. Once you've done this, it's very easy to get both computers to print to the shared network computer. You didn't mention if that printer is a wireless printer or a wired printer connection, so I have to guess. Either way, it will work now if both your computer's networking files are intact and operational.
If only 1 computer can print to the printer at this point, whichever machine can't print to it, let's say it's still the 8.1 computer, most likely that computer has it's windows networking files scrambled and must be repaired or Win8 reinstalled on it.
I have many Clients who have a mix of W7 and W8x as well as XP, Vista, W10 all working together with a network printer on a home LAN using non-domain logins.
The key here is to use the MS Homegroups feature. If you don't you are going to be spending months trying to get it to work. I've done this on other forums recently and it's not pretty. A few with very advanced expert computer skills have done so, but as soon as they repair or replace a broken computer on their home network, they have to rip all the printing stuff they did to bypass Homegroups working again from scratch!
No pretty picture there.
So, the real dilemma you have is if you are using your server to manage any of the printing of that network printer on your LAN, it's going to interfere with and conflict with anything you are trying to do with Homegroups, that is if you even set it up. I have to try and think about what you did or didn't do until we hear back from you on your actual LAN toplogy. Creating non-domain network logins for your 2 computers and unplugging your server from your LAN will allow you to use Homegroups to make your printing work easily and seamlessly.
There are lots of folks here who hate Homegroups and go to great lengths to circumvent it--and that's fine if you wish to do so; but following my recommendations for testing your printing with the Homegroups will solve your problem. If you'd rather manage that with your server fine; but if your printer will print from both computers via Homegroups, it should also print to both computers from your server managed printing resources with domain-logins on both computers also.
Hope that helps. Post back what you've got and what you've tried.
Best of luck,
<<<BIGBEARJEDI>>>