Walking on the toes or the balls of the feet, also known as toe walking, is fairly common in children who are just beginning to walk. Most children outgrow it. Kids who continue toe walking beyond the toddler years often do so out of habit. However it can indicate a problem (for example Contracture of the Achilles Tendon) and is good to have it checked.
Hip dysplasia isn’t uncommon either, sure something to have it looked at as early treatment is always better !

Did your 2 year old spend a lot of time in bouncers/jolly jumpers as a bub? I have been warned that my 7 month old now needs limited time in each as she may have problems like you describe. She could also just be exploring that this is a new way to walk. Keep reminding her to walk flat, she may just forget the tippy toes.
I would get them both accessed by a professional though in case. First step is visiting a GP or Child Health Nurse who may refer you for ultrasounds.

No sorry, don’t have any experience with this but a physio would be able to give you expert advice and any tailored exercises needed for your child.

Not sure on the hip dysplasia sorry but my 3yo daughter walks on her tippy toes a lot too. We remind her all the time to walk properly but her excuse now is that she is a ballerina and has to walk on her toes lol (obsessed with dancing and ballerinas for 6mths now and the tippy toes thing has been getting a bit worse). I have talked to my GP and CHN about it and they said to keep an eye on it but if they are walking normally most of the time that it should be ok. This was a year and a half ago though, I’m going to ask he GP about it at our next visit, just for peace of mind. Might be worth a check up for your daughter though if its something that you’re worried about

My second born had the hip dysphasia, it fixed itself after a month or 2. The weird walking should stop eventually too. My boy had turned out feet, they fixed themselves too

no i don’t know anyone who has been through this. the doctor is the best person to ask questions right now.

One known cause of it swaddling baby too tightly from their waist down. Thss was only very recently annunced as has a problem has also been found with some baby carriers you wear and carry baby in. Having said that one of my cousin’s baby was born with a dislocated hip, cause unknown. Hopefully by now the Dr. has had your baby’s hips checked…also your older son too.