You haven't provided enough information to complete the calculations, because distance is an issue. Let's have some fun anyway.
Oh, wait, the info's there after all. Sorry!
I like this site, which gives you several calculators, including one that tells you how much time is compressed given your speed relative to light.
So, we have two ships both travelling at 0.7c. the relative speed between them is zero, so they're experiencing time wasting away at the same rate. But that's not a useful point of reference. If we're standing on a planet thinking about them, on the other hand, they'd be experiencing time at about 71% of the rate experienced by us.
Now, one of the ships needs to deal with a problem ahead, so it accelerates to 0.995c. Let's assume magic occured and it accelerated instantly. Suddenly, it's experiencing time at 10% the rate of the planet.
So, from the perspective of the planet, it would seem that if ship A is experiencing time at 10% and ship B is experiencing time at 71%, so ship B should be aging at 7X the rate of ship A — from the perspective of the planet.
But all this is moot unless enough
time distance has passed to make a difference. How far ahead is this issue? How long was the 0.995c round trip?
Duh, you said Ship B spent 100 years. So, 100/7 = 14.29 years at 0.995c.
NOTE: The website I reference makes a point that's important. Light, traveling at 1.0c, experiences 100% time dilation, which means no matter where it started from, it (the photon) thinks it arrived at its destination instantly. Despite the fact that it (the photon) would have experienced a loss of energy, however small, over the distance it travelled. In other words, as Tim B II states, the relationship really is between energy states, not speed, and degeneration may be a whole lot more complicated than the math equating speed with time suggests. In other words, maybe it seemed to you like you only travelled 5 years out of an actual 50, but your body may have lost "50 years" worth of life energy anyway. It would put an interesting spin on the story, and you would join the ranks of authors who have had a lot of fun thinking about how all this manifests over the decades. But, until we can actually push something to relativistic speeds and measure what really happens, we just don't know what will really happen.
Heaven help the monkey that makes that first trip....