I don't think you would regret selling an engagement ring or wedding dress, particularly as you are separating. I personally didn't have either of those items anyway when I got married - seriously they are just metal and fabric and you will not miss them.
However, they will not make much money I don't think and they would be quite difficult to sell. Have you got any other item that you could eBay instead? Don't know how old your DCs are, but I sell everything my DCs have finished with ASAP - next thing on my list to eBay is a double buggy - things like that often make good money.
Only other thing to say is, I don't know what has happened etc, but could you approach your MIL/FIL if you are struggling to feed your DCs? I know that if I separated from DH, my MIL would help me feed my DCs in that siutaion as they are her grandchildren and she would love them regardless of me and DH falling out.