Sorry to hear you're having a tough time at the moment. I hope it all works out for you, but understand you when you say you have much to be strong for, so I hope others come along soon with some handy tips.
I'm on my own mon-fri due to dh working away. It is hard, but the kids are worth it.
DD1 was 2years 10 months when DD2 was born. I just continued to encourage all the good behaviour saying 'DD2, look DD1 is showing you how to sit nice at the table' (when she got to the highchair stage) etc.
Also involve DD1 in caring for DD2. this is time consuming but so worth it. Fetching wipes and nappies, choosing outfit, gentle sponging in bath (her job was normally DD2 feet!).
When we do interactive stuff like story time, DD1 gets MORE stories now as we have to choose same amount of stories for DD2 (double story time we call it!). Cuddling DD2 in arms, but having DD1 snuggled up beside me so she gets mummy cuddles too.
Giving DD1 quality attention when DD2 goes for her nap. And explaining when DD2 needs mummy's attention, but I'll come watch Octonauts in 5 mins etc.
Eat well. Make extra portions (of bolognaise or whatever) and freeze in portions for easy reheat dinners on 'challenging' days. If you're getting her 5-a-day into your dd, make sure you're getting them too.
So much easier if you can keep dd routine, and work baby around it until you find suitable routine for baby too. Don't stress about finding baby routine, this will come in time - just concentrate on maintaining what you've got as it's working for you.
And being nice to yourself. It's hard work but massively rewarding. Make time in the evening for you - your favourite mag, warm bubble bath, glass of wine, whatever floats your boat.
Get some early nights sleep in the evening, because you're likely to be up during the night feeding dc2. Sleep deprivation can be awful so try to rest as much as you can - tired mummy leads to grumpy mummy (does for me).
and finally, don't be a martyr - it won't help your kids. Accept all offers of help from your good family support. They want to be involved too, so let them!
Please don't think you're going it alone, it sounds as though you have some lovely family support. I wish you all the very best for when bubba comes along - enjoy the time and don't stress about housework!