I want to take distant education in a degree in B.Com in parallel with a Diploma in engineering, is it possible?

Yes, along with your diploma in engineering, you can take admission in open university for B.Com and can complete both the degrees.

As far as I know this won't be possible because for doing two courses you need to be enrolled in two different colleges, which might not be possible as you get only 1 TC. Also, the above courses are very different fields. Choose a field of interest and proceed with it.