With Tielemans, i think it's because he's not the main man attacking midfield wise. If Praet and Ndidi played deep and everything went through him then i think you'd see a different player. I think that's why we tried to play with Maddison at inside left for quite a while, to get the most out out of both of them.
Brighton will have their tails up but if we don't win this one at home then we don't deserve Champs Lge football. With the right set of results it would leave us 11 points ahead of 6th. With 5th likely to get Champs lge football this year with Man City ban (you'd imagine) unlikely to be reduced to nothing.
I'd stick with the same side that started the last game but make better use of the 5 subs rule and look to use them better to impact the game on 45, 55 and 70 mins if needed.