It's a fair trade, but I would take the two for one deal.
Both Rakell and Pastrnak are younger than Tavares. Mostly, Pastrnak hit 70 points last year as a 20 year old and he's likely going to pass his career highs and gets better as the years goes by. Rakell is likely going to be a 60+ point producer in the next few years.
Tavares let's say average of 85 points for next few years.
Pastrnak & Rakell probably an average of 140 points for next few years.
The only factor you would lose with Tavares is SHP.
Tavares by a mile, actually several miles. Neither of the other two projects to ever be a top tier player. Tavares has been, is and, assuming he gets out of NY, will be again. Even if you take what @JDawgLaSalle says, 85 pts from Tavares and 45 pts from anyone else gives you the same output as 70 from Pastrnak and 60 from Rakell. Even if you add the 10 pts to 140 total, 55-point guys are everywhere. Take (or keep) Tavares for sure.
I endorse what @musicthirsty says here completely. I didn't explain my position further with my first response because I thought this was a complete no brainer.
Don't fall into this mistake of looking at points produced by Rakell + Pastrnak > Tavares, so therefore Rakell and Pastrnak would be better to have. Comparing production from one roster spot to two roster spots makes no logical sense.
Over 100 players last year had 50 or more points, and offense is trending up so expect that number to be larger this year.
Even with a relatively deep league (you seem to imply at least 250 players will be owned if I'm understanding you), you should be able to make up that production out of the FA pool (numerous owned dman will have less than 50 points, plus of course goalies, plus presumed lack of activity and poor decision making from other teams should make this extremely likely).
Tavares is basically prime-aged. His decline is far enough in the future that considering age a factor here just doesn't work.