If one replaced Clichy, Kolarov, Sagna, Zabaleta and Otamendi in exchange for Mendy, Alaba, Walker, Bellerin*, Alderweireld and VVD, It would mean replacing 5 "Foreign Players" with 4 "Foreign Players" and 2 "Home Grown Players"*. Thus signing Mendy, Alaba, Bellerin, Alderweireld and VVD on alongside Walker on its own would reduce the number of "Foreign Players" within the squad.
However to be fair you are correct in stating that adding D.Silva, B.Silva, KDB, Sane, Jesus, Aguero and Sanchez alongisde Ederson, Lloris, Bravo, Mendy, Alaba, Alderweireld, VVD, Fabinho, Gündoğan, Fernandinho and Touré would indeed be above the 17 player limit of "Foreign Players" (if only by 1 player). However this can be addressed by selling/loaning either Bravo* or Toure to deal with issue, thus with this minor tweak it would indeed be possible to have such a backline and meet the quota.
*One of the reasons why I suggested Bellerin is that according to PL rules, he is Home Grown.
**It would however mean brining Hart or Gunn back from loan to cover the 3rd Goalkeeper slot.