"DP said just eat them or there will be hell on"
Hereby lies the problem.
I kept my 'diet' secret from my DM, who is not a complete bitch but is one who ascribes being fit, able and reasonably active (and on no medication whatsoever) but definitely slim enough (she'd 80 and just pushing into size 16s, 5'2") as being a result of her self-control over the years- as opposed to her 40 a day habit... she stopped smoking twice in her life and restarted due to weight gain, fact. I was a teenager at the time. I remember.
However, when I mentioned I was going to lose some weight, in she comes with her usual 'Well, what you need to do is..' at which point I held my hand up and said 'I appreciate your input but stop right there, I won't be taking weight loss tips from a smoker'... 
. She looked nonplussed, then tried the old 'No one fat ever came out of Belsen' 
but yes; which I counter with 'And few came out without lifelong kidney, heart and liver disease, and many developed a pathological relationship to food as a result'.
I'm not suggesting this will be helpful but it stopped my DM in her tracks.
IMHO, you need to get DP on side. He has to support you, hard that it might be. 'Win' this via calm, assertive refusal to join in on the F&C, certainly at this stage. By all means when you're well on track, go 'Yum!' Then scrape all the batter off the fish and eat 5 chips, theatrically pushing the rest away as you're Now Full, thanks.
Prawny, I am about to say something you already know, and that is you have to recognise that the act of choosing to lose weight is an act of love towards yourself, this is about YOU, not them. You only have one life, and these are the people life has thrown at you but it doesn't mean that these people's views about you are worth diddly-squat.
The people around you have 'a view' of you, one that they're comfortable with. In some families, it's 'the ill one', in some it's 'the one you mustn't upset because s/he's fragile, you know'. Some it's 'the fat one'. That's your ascribed position within the family, and you are threatening their world view and they don't like it. This might be a spur to you saying Screw You!
As an aside, I went to a seminar a few years ago about family illness, and the leader said something interesting about how some families are held together by the chronic illness of a family member. 'This is how we are and how we behave towards each other because so-and-so is ill, and we all dance attendance around that fact. DO NOT mess with what works for us by making that person well'. It manifested as people refusing to help the ill person with aggressive therapies like physio; refusing to take the 'ill' person to appointments; always fetching and carrying for that family member when in their increasing health, they could have fetched something themselves. It suits the family dynamic, the dance they create around each other, for that person to be 'The Ill One'. Increasing health would destroy that so they actively fight against the unknown.
Are you your family's 'Fat One?'