As noted in the following links:
The uplink is a single frequency where the bandwidth depends on the needs of the user (see first link, third paragraph: "The bandwidth of the single carrier is determined based on the required data rate by the user").
So in answer to your first question - No, not all users use the same bandwidth. Different bandwidths for multiple users are part of the specification (see first link: "In the frequency domain, the number of sub-carriers N ranges from 128 to 2048, depending on channel bandwidth with 512 and 1024 for 5 and 10 MHz, respectively, being most commonly used in practice.").
As for your second question - yes, the base station can serve users of various modes (ie: different FFT sizes).
EDIT regarding comment: I'm not sure how resource blocks are assigned, but I'm sure the user is told which ones belong to them - and yes, I believe the sample rates are different depending on the users bandwidth. As for the clock (from first link): "This results in a sampling rate that's multiple or sub-multiple of the WCDMA chip rate of 3.84 Mcps: LTE parameters have been chosen such that FFT lengths and sampling rates are easily obtained for all operation modes while at the same time ensuring the easy implementation of dual-mode devices with a common clock reference."