Tenants want to move into another unit

[Sam Leon]

OK I have a two bedroom unit "2" where the current tenant is vacating in January 2019.

Susan who lives in unit 4 found out about it.  Joy in unit 1 also found out from Susan.  Both Joy and Susan lives in a one bedroom unit.  They are paying $1200 each and on annual leases.

Now Susan called me and asked about being roommates with Joy, to move into the soon to be vacant two bedroom unit 2.  Unit 2 is going for $1500 a month.

Susan and Joy are pretty good tenants, have both been there 2+ years.

Normally I would gladly let them move.  However, this really puts a strain on my time.  Instead of finding one new tenant for unit 2 and turning over that unit, now I have to turn over unit 2, and as soon as Susan and Joy move in, I have to turn over units 1 and 4, and find two new tenants in January.  So all together I have three units to be turned over.  Time + Money.

Thoughts?