I have a 7m old and a 3yo. My DH is away a lot and has recently been away for 3 weeks. I have no family support nearby so it's just me and my little people quite often.
Exercise - online. I do Pilates or Yoga online during baby nap time, my 3yo plays with Duplo/playdoh/playset or joins in.
Exercise - YouTube. My 3yo loves dancing so I put on some Zumba kids videos and we dance our socks off. Sometimes during baby nap, sometimes baby in bouncer chair watching, sometimes with baby in the sling.
Self care - I shower every night before I go to bed, while both babies are asleep. Take the baby monitor and I can see if I need to speed up if baby is stirring.
Reading - on my kindle whilst breastfeeding the baby. Or in bed before sleep.
Hobbies - involve my 3yo. I love sewing. Made an outfit for my 3yo and they helped choose fabric and cut the pattern out. They sat 'sewing' next to me while I used sewing machine while baby was napping. Music - I play an instrument and whilst going to my orchestra group is currently on hold, I get my instruments out at home and play nursery rhymes on request 😂 I also take my kids to classes and groups that tie in with my hobbies so we go dancing and to a music one, too.
Cooking- meal plan based around activities noted above. Some days will be speedy pasta dinner days, some will be chuck it in the slow cooker says, some days will be get the 3yo to make it with me days. All while baby is either napping, in the bouncer chair (or in highchair in the kitchen with a wooden spoon these days) or playing on the mat in sight.
Essentially - maximise use of nap times and involve the eldest to get sh*t done.
Eat dinner with them both at around 5/530, get them both to bed at the same time, quick clean up when both asleep in bed, then the evening for....hobbies or TV.
It's actually a lot easier to manage when DH is away because I know exactly what food is in the fridge and how.muxh washing is in the washing basket etc etc