IF the tenants are on a lease, it is up to them to enquire to their landlord to find out if they can stay for another lease term prior to their lease expiring. (prior meaning enough time before, that if the landlord will not renew their lease they have time to make other plans)
If they do nothing, by law, the tenants are expected to vacate the premises on the day their lease expires.
So (your) new tenants must be out of the condo, by law, april 1st. You could have them removed by the cps on that date.
You are not bound legally to give them 30 or 90 days notice. I would call them up and tell them sorry but your moving in. Or you could be nice and charge them a months mortgage payment and let them stay until they find a new place. you will have to work some issues out with your home insurance company tho.
Either way it was very unprofessional of the person you bought from (and their agent) to not give his tenants much notice.
IF they are not in a lease but renting month to month it is a whole different senario.
this is all from the horses mouth.
Machining, Fabricating, Welding etc.