Hi sripathi,
Yes we can provide DCI for all those 4 UE's in single subframe.. No DCI in single SF is depends on aggrecation level which you use, there are 4 aggr level. agr1,aggr2,aggr4,aggr8.
If you use aggr1 then you can schedule more DCI in single SF.
Note: For cell specific DCI we have to use aggr8.(SI-RNTI, P_RNTI etc)