printing non standard size brochure

I need to print a brochure whose pages are smaller than A5 using A4 paper. I can get it to print in reduced size, but then the duplex function doesn’t work.
Can anyone help me in how to do this so that the duplex function works?

Please, follow the question at Duplex printing on other than A4 not working.

There, edit, and add the new info. Thanks.