I know a women who has x2 sets of twins within a year. So 4 the same age at one point. She isn't a single parent and children now 5, but when youngest twins were born her army husband was only allowed 2 weeks home and then was back in Afghanistan for 6 months. So 2 week old twins, and 11 month old twins.
She coped fine. However she says what probably helped was she was already used to twin routines from elder ones. And all 4 always slept well. She had them all in a routine and always woke the other twin when one woke so they were in sink. Ie if newborn twin woke at midnight, she woke the other and tandem fed and back to sleep. If one of the elder ones woke at 7am she woke the other so they would both be ready around the same time to nap etc.
She did everything like feeding and bathing and sleeping in conveyer type style. So all babies on bathroom floor naked wrapped in towel, baby in, washed, baby out, next one!
She said co sleeping was what worked best. She had both newborns sharing her bed, and elder babies shared a cot bed in her room also. She brought elder ones to her bed also if they wanted so could have 5 in the bed by morning!
She also said slings saved her. As could put baby twins in a warp together when tiny and be hands free to make lunch for herself and older babies.
Luckily she also had family and friends who would help. Not so much daily as most also working/ not super close to home, but for example I would go around ( with my own baby to add to mix), and just let her take a bath an hour alone whilst I kept an eye on them all, and her parents would go over and help cook