All of the assemblers you mention will assemble any valid 68000 opcodes with no problems.
At a guess I'd say it's most likely that the "invalid instruction" stuff you're getting is from using directives that aren't supported by the assemblers you've tried.
For example, the assembler I use (Devpac) will accept dcb.x but doesn't like the equivalent that some other assemblers use of blk.x
You could try using an assembler that supports both forms - I think PhxAss does IIRC.
Are you formatting the lines correctly? What I mean is, they usually have the format:
label: opcode.extension register/value ;line comment
Failing that, post what you're having problems assembling and I'll try to help you.
