I'm not familiar with the description "2 × 3:2 MIMO", but to answer your first part,
1) is it actually possible to have 3 receivers given that there are only 2 antennas
Yes, absolutely. One receiver connected to each antenna, and one receiver connected to both. (As long as they are receiving and not transmitting, and the right sort of dividers/combiners are used for the interconnections, they will not interfere with each other). Each receiver is connected to a different combination of antenna elements and will therefore have a different pattern.
In general, given an antenna array with $n$ elements, any subset of those elements could potentially be useful, so you have the powerset of combinations or $2^n - 1$. (Minus one because having no antennas connected is of course not useful.)