If you don’t have the mica powder try talc to keep the mold sections separated. See if you can get the unscented so there isn’t any additives.
I was looking at your figurines and you may have to do the mold in multiple sections. Make a parting line through the ears parallel with the front legs and one cutting through the tail also parallel with the back legs and set the gate on the belly with it’s own split. This will allow you to make an air vent at the tips of the ears tip of tail and bottom of feet so the resin can flow.
Maybe others that do more figurines would have some suggestions.
Because of the short working time you may want to set up the putty amounts in groups so you don’t mix the entire amount needed for the entire mold at one shot. When I used it that is what I did and it gave me time to work.
There should be some tutorial videos to explain on Smooth-on or Contenti on usage…
Make sure each of the parts is mixed (no skim of oil). Contenti’s part b is white and usually is a little oily when sitting around and needs to be mixed thoroughly then measure out each of the parts and mixed them thoroughly, You will notice the putty getting warm in your hand as it activates.
Good news about these types of silicones is they are easy to cut the spru’s, gates etc.
Down the road you may want to model the spru, runner and gate into your model once you get a good feel of how it all works for your pieces.
If your casting in one of the urethanes definitely wear gloves, There are all kinds of colorants for them. I never tried any of the epoxy or polyesters, Little leery about the odors from polyester resins.
Keep us posted, love to see the finish pieces.