Is the elastic tight round the waist.

No. I found there is alot of stretch. I ordered a medium and I'm a 10/12. They are so comfy I now have 3 pairs

Am 5 ft 2 and size 16 like things roomy, whst size can you recommend please.

I looked at the size chart provided and and also other reviews before I ordered. I'm an English size 8 but like you I like to be comfortable and these pants are designed to look good when roomy. I ordered a size Medium which covers size 6 - 10 and they're perfect. I'd suggest size XL which covers size 14 - 18. If you go larger they MAY slip down. Hope this helps.

Im 5' 5"-7" and about a size 18-20. What size would folks recommend?

I am 5ft 6 and they are very short on me I would recommend xxl

I'm not sure what size I should buy?

Generous sizing, I'm a size 12-14 and I bought size XL due to a major operation causing a very swollen tummy, I think these are true to size, and a size L would be a size 14.