be likely to - negative and past forms

[haderadi]

If you want to say "perhaps they don't meet today", do you say
- they are likely not to meet today
- they are not likely to meet today
- they are unlikely to meet today
?

And if you want to say "perhaps they met yesterday", do you say
- they are likely to have met yesterday
- they were likely to meet yesterday
?

Thanks

[Alan]

If you want to say "perhaps they don't meet today", do you say
- they are likely not to meet today
- they are not likely to meet today
- they are unlikely to meet today
?

All possible.


And if you want to say "perhaps they met yesterday", do you say
- they are likely to have met yesterday
- they were likely to meet yesterday
?

Only the first.
The second is different in meaning and fails to specify whether the action is considered to have (probably) occurred from a present viewpoint. It states simply that the meeting was considered to be a future possibility at the past time in question.

[Alan]

Yes, that is so.