Son and Moura are not wingers: they are attacking players who can - and sometimes do - play out wide. But sometimes they play centrally - even taking Kane's place when he's not available. And often we've played with only one of either Son or Moura.
The most common formation at Spurs is 4-2-3-1 … with Kane as the 1.
Currently, Dier, Sissoko, Winks, Wanyama, Skipp and Ndombele will be competing for two slots in the '2' CM part of this formation, whilst Eriksen, Alli, Ceballos, Son, and Moura and Lamela will be competing for three slots is the '3' part of this formation … Clarke has been loaned back to Leeds.
That'd make 6 players for 2 CM positions + 6 players for the 3 more attacking positions behind Kane: so if anything we'd be more over-loaded for CM than we'd be for anywhere that Eriksen plays.
Eriksen might well leave this summer (or he might not), but the loan signing of Ceballos - if it happens - would have little bearing on this IMO, because we need more 'attacking three' options in any case.