Originally Posted by Catnap

to simplify, I'd split it between modern parts that will get the bike rolling again vs. matching the original vintage parts that are on it. Vintage Shimano 600 and 105 series parts are common and easy to source on eBay, or via this forum's Classic & Vintage Sales subforum. The modern equivalents can be had from SunRace on Amazon or via your local bike store, generally very affordable (like under $100).

Without seeing a photo of your bikes, I can't say what needs to be replaced and what doesn't. Parts that aren't physically damaged in some way don't need to be replaced. They can usually be cleaned up, lubricated and re-installed. If the chains are rusted solid, replace those. If the tires are worn out and cracked, replace them (and the tubes) also. If you don't have the tools or know-how to dismantle, overhaul, and re-assemble your bikes, either take them to a shop or get ready to spend time teaching yourself how to do the repairs yourself + buying a few necessary tools.