I wasn’t sure which forum to post this and I’m sure that this has come up before but here goes. I have an RB43AH with one Ubiquiti XR2 and one Ubiquiti XR5 installed. My problem is with the thickness of the XR radios one radio has to be installed in the bottom mini PCI slot and one radio in the top. The problem is that with an XR radio in the top mini-PCI slot the MMCX connector with a 90 degree pigtail sits up to high for the indoor case. I need another ¼” to clear top of the case. Has anyone else come a crossed this and if so what did you do to solve it? 
Change one of this card to regular thickness card for example R52-350.
Yes, this is a classic example of how Mikrotik does not design for anything or anyone but Mikrotik (Ubiquiti is no better.) It is one of the many pitfalls I encountered as I started learning these things. When you are looking at websites, comparing products, and planning your projects and purchases there are many things that simply are not apparent until you have all the equipment in hand and test for yourself. Often you either end up making your own customizations or placing secondary (and sometimes tertiary) orders for additional equipment to account for these issues. I don’t want to complain too hard because this is the price we pay for not paying top dollar for Motorola, Dragonwave, and Trango equipment while still (ultimately, after much trial and error) achieving equal or better performance.
To specifically answer your question: Although RB433 has 3 slots, they are too close together to support anything other than thin form factor cards which mikrotik makes in abundance. You will either have to cut into the top of the case to make space OR purchase a custom third-party enclosure to mount your RB433 with your ubiquiti cards.
Personally, I don’t really recommend using multiple high power cards in the same RB. Too much disorder and potential for problems. But obviously it is possible as I outlined above.