Are the snowflakes jev's too? I just added a pair of young clowns with my very old pair of occ's (17 yrs) and not problems. I did put them in a clear container for two days before releasing in the system
They won't make it long term (or maybe even short term) in a tank that small. That much live rock actually decreases the amount of space for territories, clowns aren't really hiders.
Keep in mind Spike has a 180 - that's nearly 3 times the size of yours.
Clowns are super territorial, especially once they pair off. It has nothing to do with hiding spaces, but the amount of room each pair can claim as their own. You'd be pushing it in a 65 as one pair's territory will overlap the others.
Also, snowflakes are severely misbarred occys, so they are all the same species. If yours haven't paired off yet, there's a good possibility they will trade partners, so you could end up with 2 occy/snowflake pairs instead of an occy pair and a snowflake pair.
Finally, if this happenes and they do become aggressive (the older they get the more aggressive they get), you're going to be faced with removing the pair getting picked on, and that may mean one occy and one snowflake, you may have a hard time finding a home for a mixed pair.