There seems to be a few problems with this. One, it is actually disputed by some researchers that Tristram Sprague is the father of Edward. It seems the profile managers have not come up with an accurate death date for him which brings to question the possibility he is not the father of Edward. If Francis is the brother however, it would reason that is probable if Edward were born to his parents first and Francis would be the youngest., If Tristram were the father of these two there would have to be a 2nd wife because it is documented that Edward was the only son of Tristram Sprague and Elizabeth Colt.
It isn't very likely Francis was the son of Edward for several reasons. One, we know Ralph is is first son as confirmed by the Will of Edward when he says "To my 1st son, Ralph..." Second Ralp was born in 1599. Francis was born about 1590 and with Edward being born in 1576 he would only be 14 when Francis was born. Also he is not named in the Will of Edward. I read somewhere that it was possible Francis was a cousin to Ralph being that he may have been the nephew of Edward, The profiles should not be connected with out proof of parentage but theories should be noted in the bio.
This is something I will be adding as a goal to solve as part of the Sprague Name Study, I invite you to join our project and hope you will take advantage of all the resources I have compiled to aide you in your research. Please let me know if this is something you would be interested in. the link can be found below :
https://www.wikitree.com/wiki/Space:Sprague_Name_Study
Thank you for bringing this up!
Zoiya