2 of 1kg packets of BE1, that's 1200g of dextrose, and 800g of maltodextrin that is maybe 10-15% call it 15% for safety.
Dextrose is 91% fermentable so 1200*0.91=1092g, 800g maltodextrin at 15% brings another 120g of fermentables.
Adding two packs is the equivalent of adding 1.212kg (at most) of Maltose or white sugar.
Hardly enough to get too excited about the extra alcohol is going to go pretty much unnoticed, you will get some extra body from all the unfermented maltodextrin.
I'm not going to argue that a better yeast wouldn't be a good call, but we aren't out at the edges of what you can expect the kit yeast to handle.
Tony - you appear to fundamentally misunderstand how yeast works, we are adding a seed, the yeast then reproduces to many hundreds (thousands) of times what we started with, it doesn't do just so much then stop. Yeast will keep working while there is food there (sugar) and the conditions permit (temperature, alcohol, food...)
Might pay to do a bit of reading up on how to manage yeast.
But yes double (roughly) the amount of a better yeast wouldn't hurt the beer at all, just remember that there is a right amount of yeast, you can have too much as well as too little. Getting some oxygen into the wort at the start , fermenting at the right temperature, making sure all the nutrients are available... perhaps more important
In this case for a new brewer, well no need to bury them in advice nor any need for them to panic, it will brew fine and all things being equal will taste Ok - perhaps a bit too sweet - meh learning, if this is the worst that happens he's getting off lightly.
Mark