There are two things: Dual Family and DFX.
Dual Family is a game. A visual novel that's supposed to be divided into three Acts, each of them released in parts. Two+ years ago the developer actually stuck to a release schedule until Act I Part 8. Part 9 took a few months to be completed and Part 10 never arrived. I won't speculate the reason(s) for that, there's hundreds of pages of discussion here in this thread.
The developer is apparently back and working on the game, but until there is actual new content and the story progresses, your best bet is to assume it's a way to build up a patron following to milk them later.
DFX is a brain fart released to troll his supporters. Its name is based on Dual Family and part X (part 10 of act 1) which people mistakenly believed would contain sex between the main cast*.
I believe DFX Act I was released to troll the support base. After losing a lot of patrons, gumdrop apparently realized they're not as dumb as he thought they were and started working on his actual game again.
But to keep up appearances, he's still working on DFX and made Act II of it now.
At least that's my understanding of what DFX is. Ignore it, don't touch it, prove that even freeloaders have their limits.
*) Yes, for some dumb reason or another, a lot of people assumed the game would come in ten installments. Nine to build up the tension and ten to release all of it. Never mind that gumdrop himself said it's going to have three acts, each containing multiple parts. The first act is almost out. The second act is supposed to be romance and the third act is supposed to be sex.
Assuming each act is ten parts, that's a total of thirty installments, and only the last ten have any chance of sexual content. People still assumed that the game will have just ten parts and even though parts 1-9 only set the mood for romance and maybe progressed 3% towards sex, they still believed part 10 would cover the remaining 97% and culminate with multiple sex scenes.