So I'm just learning Latin, and I'm not sure if I got this translation right. Whenever you use 'in' in Latin, the predicate noun is refers to and the noun the follows it has to have the same form right?
Let me know if I made a mistake: Fōturnam multam in tuam vītam fīllarum vidēmus, meus amīcus.
Your translation is certainly in the right direction, but it needs some polishing:
I'm not sure whether multam is a good way to say "great" here. You could also consider magnam, grandem, tantam. You can compare these words in any online Latin dictionary. I wouldn't say multam is wrong; it's just that there may be better options.
If you want to say "in X" (location) rather than "into X" (movement), the word following in should be in ablative rather than accusative. As an anonymous suggested edit mentions, you might want to change vita ("life") to plural as in English. You currently have singular accusative. The singular ablative would give you in vita ("in the life"), whereas in plural you'd have in vitis ("in the lives").
There are typos: "daughter" is filia, not filla, and "fortune" is fortuna, not foturna. (Some words do have legitimate spelling variants, but I haven't seen these before.)
The word tua modifies the daughters. After all, it is the filiae that are yours, not the vita. Therefore tua should have the form of the noun it modifies: tuarum. Because these two words go together, it is natural to place them next to each other, although it is not necessary.
When you address someone, the addressee is not in nominative but in vocative. Therefore meus amicus should be mi amice.
If you want to keep track of vowel quantity (which is a good practice!), the a in the plural genitive ending -arum is long.
With these corrections, your sentence becomes:
Fortūnam multam in vītīs fīliārum tuārum vidēmus, mī amīce.