Long live for all of developers who dedicate their time for humanity.
First of all I want to thank to all of you for your nice response. But the bad things is I'm not a computer programmer. I'm just a computer user (maybe advanced user) who tries to give idea about open source development. I love open source software as they help me solve my daily problem in my job (I'm a teacher). Both FreeBSD and LXDE are one of my favorite software.
When I heard news about desktop environment project in FreeBSD it gave me idea to combine it with LXQT. In my point of view, both PC-BSD and LXQT are share same goals (full featured, qt-based, light-weight DE). The only thing that is different are the way to achieve the goal. Just like mentioned by PC-Man, the biggest obstacle to achieve the goal is licensing issue. It is one of the reason for me to give suggestion to LXQT developers about LXQT licensing policies. AFAIK, there is no problem for FreeBSD developers to use non-BSD license as long as it isn't strong copyleft (e.g. GPL, AGPL). My conclusion is LGPL is the best license to narrow the gap as FreeBSD developers seems don't have problem in using Qt and other LGPL libaries.
The only thing that I can do is to pursuade LXQT developers and PC-BSD developers to start initial discussion about everything that make colaboration between two projects become possible. I can test the software, but only as an user, not developer. I cannot make patch, compiling, etc. The only thing that I can do is giving idea and advocating which I hope can benefit both project.