It's a big potential trade, with a lot of moving parts.
First, I view Bell and Lacy as more or less the same. Both are definitive RB1s. While I think Bell is ever so slightly ahead of Lacy, they're still top 5 guys. They basically cancel each other out in my eyes.
Looking at Jeffery and Adams for Cooks and Landry, it's an interesting 4 person swap. Jeffery is sort of a low-WR1 candidate, while Adams is more of a low-WR3 to mid-WR4 option (depending on league size). Cooks I feel is a high WR2 option, and Landry is a high-to-mid-WR3 option.
From a value standpoint, it's pretty close, and whether you prefer the first or the second option I think depends on the rest of your WR group. The move on paper looks like a depth move, you're adding a WR2 and WR3 in exchange for a WR1 and a WR4. If you've got another potential or probable WR1 and nothing besides Adams and other chaff behind him, then it's a good move. If instead you're lacking a WR1 besides Jeffery, but have a WR2 and WR3 already, you might be adding more starting talent, but will lack top end talent to push you over the top.
As for Blount and Blue, it's dependent on Foster probably more than anything. I don't really trust any NE backs beyond spot fill-ins, and even then it's got to be whichever RB happens to be hot at that moment, but I also don't trust Blue to be even remotely relevant past whenever Foster returns. Reports are that that's around week 9. Maybe Foster gets hurt again, maybe he takes 90% of carries and Blue disappears almost entirely.
Both are major gambles.
Personally, I'd probably lean a little towards making the trade, but that's from my default view, double check your WR depth and see where you're at in terms of what I outlined above. Bell and Lacy cancel out. I like starting depth over top end talent with no backup tools, so I'd probably go with Cooks and Landry. With Blount and Blue, I wouldn't expect Blount to be a major force for more than 8 weeks anyway, NE RBs are always seemingly fickle, so if that's the case, I'd probably opt for the guy who is in the offense that ran more than 50% of the time in 2014 and is directly behind a guy who, while skilled, is clearly injury prone, and is likely to get around 8 weeks to start the season.