Testing isn't foolproof.
There are false negatives to start with.
Not to mention that the STD tests all only detect STD's some period after exposure.
Most STD's are detectable with high certainty rates only 7-10 days after exposure.
Before that they can be undetectable, but still transmissible.
With HIV, the test latency period is 21 days...
So basically, the test is at best a confirmation of a problem, or an indicator of unlikely to be a problem.
It's not a guarantee for you unless you and the two ladies all abstain for the latency period, then test, and don't have sex until you meet.
Which given they're WL's with partners, well it's not going to happen!!!
If it was me, I'd do it.
But it sounds like you are way too risk averse for this...