Three teammate outfielders, 30 home runs each, same year: 1941 Yankees, 1963 Twins.

It's been done only those two times.

1941 New York Yankees

Rk	Player	HR	Year	Age	Tm	Lg	G	PA	AB	R	H	2B	3B	RBI	BB	IBB	SO	HBP	SH	SF	GDP	SB	CS	BA	OBP	SLG	OPS	Pos
1	Charlie Keller	33	1941	24	NYY	AL	140	610	507	102	151	24	10	122	102		65	1	0		3	6	4	.298	.416	.580	.996	*7/H
2	Tommy Henrich	31	1941	28	NYY	AL	144	632	538	106	149	27	5	85	81		40	5	8		6	3	1	.277	.377	.519	.895	*98/H
3	Joe DiMaggio	30	1941	26	NYY	AL	139	622	541	122	193	43	11	125	76		13	4	0		6	4	2	.357	.440	.643	1.083	*8

Provided by Baseball-Reference.com: View Play Index Tool Used
Generated 9/20/2016.

DiMaggio hit in 56 consecutive games in 1941. He had the highest batting average (BA) each of the two previous seasons. He hit at least 40 home runs (HR) for the only time in his career when he led the American League with 46 in 1937. 1941 was DiMaggio's fifth consecutive season with at least 30 HR. He did it twice more after WWII: 39 in 1948, 32 in 1950. In 1941 he was AL MVP for the second of three times.

Keller was on his way to the Hall of Fame only to be derailed by injuries. He had at least 30 HR two other times: 31 in 1943, 30 in 1946, Keller's sixth and final full season. Keller had OPS+ 152 but in only 4,604 plate appearances (PA).

Heinrich was way above his norm. His closest HR seasons:
22 in 1938, his first full season
25 in 1948
24 in 1949, his final full season, age 36.

Catcher Bill Dickey was the only other 1941 Yankee in double figures in home runs: 24.

1963 Minnesota Twins

Rk	Player	HR	Year	Age	Tm	Lg	G	PA	AB	R	H	2B	3B	RBI	BB	IBB	SO	HBP	SH	SF	GDP	SB	CS	BA	OBP	SLG	OPS	Pos
1	Harmon Killebrew	45	1963	27	MIN	AL	142	596	515	88	133	18	0	96	72	4	105	3	0	6	16	0	0	.258	.349	.555	.904	*7/H
2	Bob Allison	35	1963	28	MIN	AL	148	626	527	99	143	25	4	91	90	2	109	3	1	5	7	6	1	.271	.378	.533	.911	*9/8H
3	Jimmie Hall	33	1963	25	MIN	AL	156	571	497	88	129	21	5	80	63	4	101	0	9	2	8	3	3	.260	.342	.521	.863	*8*7H9

Provided by Baseball-Reference.com: View Play Index Tool Used
Generated 9/20/2016.

In 1963 Killebrew led the AL in HR for the third of six times, including the previous and next seasons. In 1969 he matched his most HR and had his most RBI, leading the AL in both with 49 and 140 and was AL MVP.

Allison hit 30 HR in 1959 and was Rookie of the Year. He hit 29 HR in 1961 and 1962. Allison hit at least 30 for the final time in 1964: 32; however, Allison mostly played first base for the Twins in 1964.

Hall had never played in the major leagues before 1963. His HR in his first five seasons: 33, 25, 20, 20, 16. Hall was never in double figures again.

1964 Twins HR leaders:
Killebrew 49, in his final season in left
Allison 32 but at first base (1B)
Tony Oliva 32; Rookie of the Year OF; next highest: 25 in 1966

In 1962 Killebrew hit 48 HR, Allison 29.
In 1961 Killebrew (1B) hit 46 HR, Allison 29.