It strains my 4th finger to bend it inwards is all and I can't maintain a relaxed hand at all. Do you think that taking it very slow and practicing repetition with smooth movements of the hand can work?
For now I've found that jgranata13's suggestion to take 3 on the B# works best for me.
That's perfectly fine! My idea was mainly to explore how to use the more difficult fingering, because in the future you may encounter situations where crossing 3 and 4 is the best or only available solution. (Examples include Chopin op 10 no 2 or op 25 no 6, for example).
I can try to give you something to play with that may help you figure out what to do:
First try playing only C sharp with a perfectly relaxed and comfortable hand. Pretend like you don't know you'll have to go to B sharp with 4 in a second.
Then, move your hand so that your 4th finger ends up in position over the B sharp, without having to bend it inward. Keep the hand and wrist very relaxed and comfortable as you do so. At some point you'll need to let go of the C sharp or you'll have to twist your hand or bend your 4th finger a lot so just let yourself do so.
The key is to stay very relaxed and smooth, and making the movement feel natural and easy. If you feel like you need to bend your 4th finger inwards in an uncomfortable way you need to help your finger out by moving your hand instead of the finger. When you can do this quickly and smoothly it'll basically be and sound legato.
When you add the chords held with 1 2 you'll basically do the same thing as above. Ensure that you are still keeping your hand very elastic and relaxed.
Let me know if this helps.