network connectivity issues downstairs all of the sudden.

we moved in recently to this place about a year ago, and according to Xfinity, the only viable connection was the one upstairs. my mom personally didn't care, so, we have the modem/router in my room, next to my PC.

however, in the past two or so months, the downstairs has been having network connectivity issues. i know what the problem is. the PCs being used downstairs are both 10-15 years old, and i'm pretty sure both computers are still on Wifi 4, and of course, the degraded signal from having to travel such a long distance and through so many obstacles.

is there anything that i could possible do to alleviate the issue? i've tried moving the modem, but only the upstairs coax works. i looked into alternative solutions, and MoCA seems like it'd be the best, but, based off how it works from what i've read, it doesn't seem like it'd even work.