Landlord asking for Help

So our landlord has asked if my fiance and I could fill the basement apart with tenants for him and his wife since they just had a baby. This would include advertising and doing viewings, he will cover the proof of employment and signing the lease portion.

Neither my fiance or myself have any issues with this, but he wants to find someone so the switch between the current tenants and the new one is relatively close. That means I’ll have to provide notice to the current tenants that I’ll be doing showings on his behalf. Is this legally allowed, and do the current tenants have any say in whether or not I may enter the apartment on his behalf.

I think normally this wouldn’t be such an issues but the current tenants aren’t the nicest of people and would create issues with timing for viewings.

Thank you for any advice!