(去火星)
我不知道你在火星上的原因;但我很高兴你在那里,我希望我与你们同在。
"Whatever the reason you're on Mars is, I'm glad you're there, and I wish I was with you."
This one is very good speaking of order of phrases.
PS
'不管'is often used in Chinese (both speaking and writing) which means'whatever''wherever''whoever',etc.
For example,
Whatever you say, I won't change my decision.
不管你怎么说,我都不会改变我的决定。
(去火星)
不管你为什么在火星上,
[ if you mean "I don't care why you're on the Mars", this is the word you should say, other wise: 不知道你为什么在火星上 for "I don't know why you're on the Mars." ]
我都很高兴你在那,
[ use "都" for whatever ]
我希望我是和你一起去的。
[You used "was" so "是" and "去的" for past time, ]
(去火星)
我不知道你在火星上的原因无论你在火星的原因是什么;但我很高兴你在那里,我希望我与你们同在。
"Whatever the reason you're on Mars is, I'm glad you're there, and I wish I was with you."