Yes, it's a bad Idea. Do you mean 2 plants in the same pot? You are asking for trouble, it'll be to hard to workout feeds 1 plant will take more than another as dif strains sure even the same strains take dif levels of nutes. And if you run into 1 def on 1 plant it'll be on the other. I don't even l8kr the idea of a fixed DWC/RDWC as 1 plant suffers they all do. Sep pots for Sep grows pal. Also, 6.5l pots is very small. You should be aiming in the range of 8-11l for autos and 11-14l for fems. Also try a root stim it'll transform your grow. Root growth on the b9ttom is like a mirror to the top. The more room roots have to spread out grow the better the size/height/harvest of the plant as a whole it's just better. Please don't put 2 plants in the same pot, or do. But trust me, without even attempting it's a bad IDEA. Yoi say you got tight time, well if you do thst you wont have any time, cause all youll do for urself is make problems. Happy growing good luck.