End of lease is largely meaningless these days as you have to give notice based on the RTB rules regardless of whether the lease ends tomorrow or whenever.
As Far as I know - and I don't know much about Lease agreements, so let someone else validate this - but these days, the lease really only ties the landlord to a longer agreement. Under RTB rules, once the tenant is in for over 6 months, they're there indefinitely. The exception here is the residual tenants that are working through any outstanding Part 4 period, be that 4 or 6 years.
As to issuing the termination notices, you should issue them as soon as possible, making sure you're within the RTB rules (and your lease agreement - if it extends past that time) for each individual unit. You might consider having an aligned date across the units, but be very aware that some tenants might sit and you may well be stuck with a portion of your property empty (and not generating any income / reducing your costs) while you wait a very long time to get any sitters out.
I know directly of a case (which occurred 20 years ago, before all of the new rules etc) where 5 of 6 tenants moved out per the notice agreement, and the last sat for over a year. She was brought to court, had an attachment order made against her salary, and yet still never paid a penny rent or compensation from the point the Notice period was up (i.e. a full year of stolen rent for her unit, as well as lost revenue on the other 5).
Good luck, I hope your exit is clean.
Who'd be a landlord, eh?