We use TS's a lot and don't have any issues.
What's your LAN/WAN like?
Running FM Server?
What are the stats on the TSs? (Assuming not all that great since you have a "couple" for only 10 people)
Specs of one of the TS servers is:
Quad Core Opteron
STRIPED RAID HD's
The weird thing is, the Terminal server is really reactive for the other applications on there but filemaker can be a bit ropey!
Our WAN is an 800K DSL VPN via Cisco ASA5505
What connection do you have between the TS & FM servers?
FM and TS servers are on the same switch.
3COM gigabit layer2 switch
all CAT6 cables