Their value is only as working rifles in less than the most popular calibers.
Generally, collectors are only interested in rifles in their full original military configuration, and the market value of fully sporterized milsurps is long gone as well. Full custom jobs from expert smiths, with great wood, full reblue, custom metalwork, all quality work, not Bubba in his garage, don't bring anywhere near the value they once did. Those guns rarely bring $500 these days, and I've bought several in the last decade or so for $350-450 (with scopes) and your guns aren't worth that to the current buying market.
You might get $300 but I doubt it. People just don't want those guns anymore, unless they are going to use them for a hobby project, and if so, they certainly don't want to pay much for them. Essentially the market value of your hand me downs is the value of their actions. The peep sight on the mauser MIGHT be worth more than the rifle itself, to a special collector.
The market is weird that way.
If you're looking for a cash value, a couple hundred, or so, their value as a usable rifle is more than the cash they would bring in today's market. Their value as heirloom pieces is priceless.