Congrats.
We just recently closed on a SFR and Duplex the same day and within a day of closing we mailed out a letter informing the tenants of the new owners.
Letter also stated we would be stopping by to introduce ourselves, getting contact info of tenants and since 2 of the 3 were M2M we would be giving them the option to move or to sign a new lease with an increase in rent. The tenants didn't balk at this because the listing agent let them know the house had sold.
In our mailed letter and when we met the tenants we handed them a copy of the same letter that gave them 3 ways to pay rent in the future.
If you haven't yet ask the tenants to fill out an Estoppel agreement on the units,you should, maybe you can even get the sellers to fill this out at closing. This will be good to know what you bought that is inside or outside the units. The homes we just bought the tenants own the range, dishwashers, washers, dryers and fridges. Good for us we do not have any appliances to repair.