Handling a number of simultaneous measurements in Extended Kalman Filter?
If your measurements are batch, so is your filter.

You can do a number of things.

You can sequence your measurements in natural order and update the filter for each.

You can do the previous and then approach the problem as a fixed lag smoother.

There is a literature on out of sequence and delayed updating as well, like: 


  Ensemble Kalman filter for multisensor fusion with multistep delayed
  measurements Sirichai Pornsarayouth; Masaki Yamakita
  
  2011 Aerospace Conference Year: 2011 Pages: 1 - 10 Cited by: Papers
  (1) IEEE Conferences