Do Gather The Townsfolk's (or cards like it) tokens go on the stack separately?
Tokens don't go on the stack, only spells and abilities. Gather the Townsfolk creates both tokens simultaneously.


You cast Gather the Townsfolk.
Gather the Townsfolk resolves:

Put two 1/1 white Human creature tokens onto the battlefield. Cathars&#39; Crusade's triggers twice.

Cathars' Crusade's ability is placed on the stack twice.
The second instance of Cathars' Crusade's ability resolves:

Put a +1/+1 counter on each creature you control.

The first instance of Cathars' Crusade's ability resolves:

Put a +1/+1 counter on each creature you control.



Both tokens (and any other creatures you might have had) got two +1/+1 counters.



As for your second question, someone casting a split second spell would not change anything.

A split second spell between steps 1 and 2 would resolve before step 2, then you continue with step 2. Same goes for one cast between steps 3 and 4, or between steps 4 and 5.

Split second merely stop you from casting a spell or activating an ability in response to the split second spell.