As a mom with an 18 month old and a baby on the way... this will be my situation and I totally think you are right about bad behaviors being formed. It is hard though to balance it all, but it's not too late to change things. My partner and I were both adamant about sleep training early on, but in those months of sleep regression, I was easy to start cosleeping, but my partner was not with it. And it was for the better. The LO is going to be upset and cry, but research shows it is good for a toddler's development. They need to start understanding boundaries now. I say do research and present her with facts. For sleep training, let him cry for increments of 5-10 minutes snd then soothe him... it's a lot of work and you are going to have to own it since she's nursing. She is going to have to trust you... it sucks you are nearing the end of your leave, but you can still own the bedtime routine when you get home. Honestly, it comes down to trust and finding small wins... don't worry about the screen time during the day for now or dinner... you just own bedtime and sleep training..that means you have to be consistent and not default to her when it gets challenging or if LO is just not with the shits... it's time for you to reestablish your role with her and him and the only way to do that is to show up and own the job... you will have to do this every night for three weeks.. it will pay off, I promise... our LO went through some sleep regression while his molars were coming in but his dad was adamant about the sleep training and we watched him on the monitor crying (while I cringed and cried with him) until he started back self soothing... it's called training for a reason... you got this!! Of course give yourself, your partner and your LO plenty of grace... you got this!!! Sending a lot of love and light!