Well pressing your fingers down hard doesn't strike me as a good idea.
As with all cello - No tension. Anywhere. I know it's really hard hard not to grip like crazy at first, but you really need to keep it all as tension-free as possible at all times.
I'm not really sure what you mean by 'ALL double stopping'. But, for what it's worth, I'd suggest starting on the C and G string in first position, playing two notes slurred on a down bow, followed by the double stop of those same two notes on an up bow. That way your hand ought to be in the right position to get the two separate notes ringing cleanly anyway. 1 and 4 can be more difficult to execute properly as the little finger tends to be weaker . In addition, you're stretching it away from the main part of the hand and the other fingers. It'll strengthen with practice.
Check that you're not squeezing down with the bow, gripping the neck or pressing down overly hard with the fingers on the strings. And take it very slowly.
Hope that helps a little.
It seems you posted while I was fighting my machine
Playing separate notes (with a slurred bowing) followed by a double stop will help you to hear the notes and will also help with motor memory-i.e. making sure that the hand is in the correct position and that you have the right fingers down. Just make sure not to be in too much of a rush. Do everything very slowly. Aim for quality of sound in one position before rushing off to complete every double stop across the fingerboard