Hi,
Being receiving antenna it's not that critical.
Bigger antenna should be behind smaller one pointing to
same direction.

Nope!

The one in front may well "shield" the one in back.

Insofar as reasonable they should be next to each other with a line between
the two masts being perpendicular to the line to the signal (the TV station
antenna).

They should be separate at a minimum by the longest element of either
antenna. That's the element furthest away from what the antenna is pointed
at. (That's on the order of 4'.) IOW: no part of either antenna should be
closer than 4' from the other antenna. If you "do the math" that means you
need a space of about 12' side to side to mount the two antennae.

Frankly, you would likely be better served is you just mount the larger
antenna and install an antenna amplifier at the antenna and then an
amplifying splitter in the house to feed you TVs including splitters added
to permit moving the sets about.