You are doing a great job! Twins are hard enough, and older children to manage as well make it really tough.
Mine were 5 and 3 when my twins were born, and my DH works away part of the week so for 3 a week days I'm totally on my own. I also breastfed mine, exclusively for 4 months, then mixed.
Have a think about what you find hardest, and see if you can tackle that. (I didn't have much help, but knew school runs would finish me off, so I got help for that until about 5 months. I also think running to and from school every day is not going to help with milk supply, so you might want to tackle that).
Here are some ideas, some of these we managed, others we didn't:
Reduce your school runs - ask another parent if they could take/drop your child even once a week. Or advertise on gumtree for a student to do school pickup, it would be fairly cheap. By not doing school run you save some energy and time that you can be doing something more important!
Your parents work full time, but could they bring you a batch of food at the weekend, or come and clean once a fortnight?
As pp said, don't iron anything. And no need to be obsessive about cleaning either!
Do you have a local twin group? Mine is amazing for providing practical support - mums of older twins will often help out a mum with twin babies.
Tandem feed if at all possible. It saves time and keeps the babies in synch. Do you have a twin bf cushion? They are lifesavers, I couldn't have done it without mine. Again, my local twin group loans them out so you don't have to buy one if you are short for cash.
Routines - up until 4 months I didn't have a set routine but just operated on 3 hourly feeds. 4 months is a reasonable time to introduce a routine I think but don't worry about it too much. And if your babies don't suit Gina, ignore her! She doesn't let them sleep long enough, IME.
Bottles - this is a hard one. My older two were bottle refusers and it made me feel really tied and stressed, so I was determined to get my twins drinking from a bottle. At the same time, washing and sterilising expressing stuff and bottles while also breastfeeding nearly finished me off!
This is what I did. I'd express a bit after each feed and freeze the milk until I had enough for a couple of feeds. (tip from HV - you can put the expressing equip in a freezer bag and keep it in the fridge between feeds, then only wash/sterilise it once per day). Then when my DH was around I'd get him to give the babies a bottle. If they took it, I would then express that feed and store for next day. If they refused, I'd feed them directly. Once they got used to taking the bottle I'd express about 30 mins before feed was due, let DH give the bottle and I'd go to bed.
Sorry for the long post. It does get easier, and as difficult as it is with 4, I can already see how much my kids love being part of a big family.