Hi OP
I haven’t read the entire thread, but I wanted to say that fussiness is completely normal. DC may be trying to push boundaries at this age too.
Maybe skip pudding out a couple of days a week. Don’t let DC expect pudding after every meal as it creates the idea that they want to save room for sweet treats.
If you don’t think they’ve had enough, then bargain for 2 more mouthfuls etc. My dd is doing this a lot, but I’m super conscious about creating food issues in later life. No one should leave the table until the last person has finished, so definitely don’t leave them to eat on their own. From experience, this is very negative for children.
If it’s new food, my rule is that they don’t have to eat it, but they ALWAYS have to try it. You need to encourage a love of food so they see it as an adventure, rather than a punishment to eat all the good stuff, and not see sweet treats as a reward.
I would also try and balance your approach with DP. If you can’t agree, then make it a special meal time for when DC is with you, and an equally special meal time for when he is with DP. For example, my DP lets ours have fizzy drinks and junk food. I am majorly against this, so the deal is that if I’m out one night, it’s a special night in with DP that they get to lounge about with pizza. Then when DP is out, DC and I cook dinner together and they get to pick what we have, so it’s a fun experience, where they eat absolutely everything, as they helped choose and make it. Being involved with cooking seems to really engage them to eat it as they are super proud, and the focus is on the main, not treats.
It sounds like you’re really conscientious, so go with your gut on this. If you don’t want to do the same as DP, then choose your own style and stick with it. Try not to stress about it though. DC will be fine so long as he has a balanced diet between the two of you. This will create the happy medium you’re looking for, and no need to start an argument with DP over it. Respect his approach, and do what works for you x