Tasker has some problems in this regard (at least in my experience). I send messages to about 60 - 70 members of our club on a regular basis using SMS. I use a second device (like a spare tablet) and use Join to send a message to my phone. There is send as an SMS in Join that I use to send the message back to my phone and it sends it out in groups of 20 (a strict limit set by my carrier).
One of the problems you mentioned is sometimes Tasker sends a message to wrong numbers. This is a problem in Tasker. The work around I found is make sure all numbers in each batch are in the same area code. If you send 15 numbers to say a 709 area code and 1 to a 530 area code, the 530 number says it sends correctly, but it will go to the 709 area code, despite what it says.
Yes, Tasker will work great if you send the message manually, but will have problems if you send as a batch. Try a second device and join. If you need help, let me know. I'm not home this weekend, but I can get the info on Monday.