...that two players have met in all the calender majors in one year
1981 FRENCH OPEN CLAYS H. Mandlikova7-5 6-40
1981 WIMBLEDON GRASS. Evert 6-2 6-2
1981 US OPEN HARD Evert 6-1 6-3
1981 AUSTRALIAN OPEN GRASS Evert 6-4 7-5
In looking back at draws I can't find another instance of this happening where 2 players played each other at all 4 slams in one year. I don't think there's much chance of this having happened during the Open era of men's tennis. The ladies always seemed to be more consistent in reaching the latter stages of the slams. I remember Graf and Coetzer meeting many times in slam play from 1994-1997 but not at all 4 in one year.
I once looked into the rankings discussion for 1981 because it was so odd that Hana made 4 slam finals in a row, won 2 of them, but could never rise above #5 in the rankings that year. It was her misfortune to draw Chris so often, and what probably rankled them both was that they had to meet twice in the QF's because Hana's ranking didn't make much sense. Many thought Hana should've been #2 and I personally think she should've been at least 3rd.
You still have to win them all no matter who you play. But I'm pretty sure that's also the only time that's ever happened to any man or woman. So your question brings up what I believe are two extremely rare situations.
What's even more intriguing is that Evert and Mandlikova also met in the finals of the 1980 US Open and semis of the French that year. So for the 1980-1981 seasons, 8 majors, they faced each other 6 times. Also, Evert didn't play the 1980 Australian.
Intriguing indeed.
Serena and Venus did meet in 4 consecutive major finals from 2002-2003. Chris and Martina met in 3 consecutive major finals in 1984, and in 3 of the 4 in 1985 (Hana preventing another Chrissie-Martina final in the 1985 US Open).
As far as the rankings in 1981, it was when the WTA used their really quirky ranking system they never explained and no one ever really understood. And 1981 was also one of those years when the top 5 all had very good records. Chris was the queen of consistency and maintained #1 throughout. Late season surges by Austin and Navratilova kept them in the hunt for #1, and certainly placed them as solid top 3 players. Hana was terrific in the majors, but the 2 QF losses hurt her. Andrea Jaeger had a great season, and overall was more consistent than Hana, which is probably why she wound up ahead of Hana in the rankings.
It was tough that Chris and Hana had to meet in the QF of the 1981 US Open, a repeat of the previous year's final, and that year's Wimbledon final. It's why I so wish the USTA had the balls to deviate from the rankings the way Wimbledon did that year, and seed Hana higher. It was kind of a joke that Andrea Jaeger was #2 seed for the US Open. Through a quirk in the rankings, Jaeger was ranked #2 for all of 2 weeks, during the exact moment they announced seedings for 1981 US Open. (Even though Hana had beaten Andrea in the semis the year before). Unfortunate too that Jaeger crashed out in the 2R of the Open, and Chris and Hana were drawn in the same quarter. Really would have been an even more intriguing event if Hana were in Jaeger's quarter.
At the Australian, where Hana was defending champ, she was again seeded #5, and again drawn against Chris in the QF. Jaeger, again seeded ahead of Hana, didn't live up to her seeding. (At 3 of the 4 majors in 1981, Jaeger failed to live up to her seeding, and in the only major where she fulfilled her seed, the French, Hana won the tournament.)
Another commentary on the Evert-Mandlikova match ups in majors is that they faced each other 13 times from 1980-1986. Believe it or not, that is the same # of times that Chris and Martina faced each other in majors. Evert held an 10-3 edge over Hana in the majors. Chris was obviously the better player, but too bad for Hana. Chris and Hana met in just 3 finals from 1980-1986, compared to the 11 finals Chris and Martina played in.