Our oldee LO was only 3, but the first month or so was absolute madness and I felt like I couldn't tell anyone. He hit so hard (and aimed for the face), ripped my nose piecing out, meltdown after meltdown, barely slept... and we had literally just become parents and could hardly keep a coherent sentence in our heads some days. Then his little brother joined a month later, and it was just... constant. Hitting kicking, biting, the lot. Some days I was basically a bouncer.
I agree routine is important- if you can spare half an hour, write it out for yourself, but keep it low stakes and remember you are all not only learning about each other but you are learning what it takes to get kids out the house and going. However, other stuff that helped us in the early days were:
Throwing beanbags to replace the cars lobbed at us
Reducing the amount of toys and stuff on how or available to be thrown hit or jumped on
looking up safer restraints and speaking woth our social workers about how to use them.
Basically living outside at our local park (we had 2 Park visits a day, minimum for the first two months)
Screen time was completely up for grabs whenever we needed it to regulate. We gave them both old phones with bbc iplayer installed and they watched hours of Mr tumble and paw patrol
Going back to basics with food for the kids. They ate the same thing at the same time for months because they knew it would be predictable and it reduced stress for everybody
Sleeping was tough for us, so we had a night on night off system
Reach out to your local children's homestart or sure start centre, library, playgroups etc. Honestly, ours were great, and ran stay and plays for kids up to 5 and some for older kids as well even furing summer, and more to the point they were specifically accepting of or kids even though they were a bit wild and hit anything in sight. We went to loads in our first weeks together, they called me mum, which made me cry a bit, but it made me feel like mum too.
Divide and conquer where you can- get ine busy and regulate the other. I also keep mine physically separate if they are aggressive, and have the jnfrastructure set up for it (2 stickers on my car for them to touch whilst I get the other into the car so they can race but not touch the same one, they sit in the same place at the table far away from each other etc)
Also think about your house set up. We eventually said they were only allowed in the same room as us - so now we basically come downstairs before breakfast and nobody goes upstairs in the day, we bring down whatever we need and then they never go upstairs in the day whoch prevents them hurting each other in a different room. Or maybe they need a bit more space- could they hill in their own rooms? I found I was kind of smothering the eldest, which meant he was stressed with me. When inreduced my communicating with him, it really helped.
Sensory play stuff helped ours- play doh and flour mixed with pasta on the floor kept ours regulated for over an hour on one of the very early days when he was constantly hitting his brother.
Get a robot vacuum cleaner if they are messy. Honestly the best thing I have ever done. Clearing up rice from sensory play is much easier when you know your lil robot friend is there to help you
However, overall, you are not far in, and basically i would say do what it takes to survive. Have your basic 2-3 word rules, repeat them often whilst affirming yourself and steamroller through it. Reduce your expectations if what will be achieved and remember the only thing you have to achieve for the next month is keeping everyone sane and alive. If that means you go to the park every day, do it. We drove to different parks every day, made a list on Google maps and tried them all out and rated them. But that was all we did. Literally the whole day whilst I repeated to myself and to him: hitting is not allowed. Ita pur job to keep all our family safe. Hitting is not allowed.
We really didn't want anyone round us in the early days because we we didn't want anybody seeing us in the state we were in, but of you can stand it, rope someone else in to help bring food or do laundry or whatever.
You mentioned not being able to access support networks, but even of it just to meet another frown up at a park as if you were strangers can help you feel regulated because your kids probably don't know them yet. A possibility worth considering if they ca deal with the subterfuge.
Basically, take care of yourself, respect your own hard boundaries and lower expectations of whatbyou and your children can achieve. Anything additional is bonus!