Ghosts/spiritual activity since having baby?

Any ghost/spirit experts?

So we moved to a new house (we own) in January. Living area is downstairs, bedrooms are all upstairs, which is carpeted. It's a fairly new construction and it was sold to us by owner...single woman, original owner, no kids...she bought the house post divorce, both her parents are still alive, she sold it when she got engaged to a new man and moved in with him, so no one died in the house. I checked everything out and her story adds up to everything she told us, we even met her fiance.

Had our 4th baby end of April, so we had been living here about 4 months.

After she was born I started hearing noises like footsteps next to my bed and baby's pack n play, and heavy footsteps coming from upstairs while downstairs and no one was up there. At first I thought I was just going through post partum or sleep deprivation and it was my imagination. But my husband sleeps in a separate room (we have a good marriage but he sleeps in his office since having the baby) and he's heard it many times as well. He started asking things like "did you come in my room in the middle of the night? It sounded like you were walking by my bed but I woke up and you weren't there?" Even though we both heard it, we still chalked it up to sleep deprivation for awhile, but now baby is only waking once a night so we aren't that sleep deprived.

So then my mom came over yesterday and heard footsteps upstairs and said "oh, your son is home from school today?" but no one was upstairs. And we've also had doors inside the house close by themselves (we never open windows so no drafts) and the latched gate in our yard a couple times opens and closes by itself. My mom said maybe it's a spirit connected to the baby since that's when it started, like a relative or something. The spirit or whatever it is doesn't seem menacing, but this past month, it wakes up myself, my husband, and the baby almost every night with footsteps, and it's getting annoying because the baby doesn't sleep through the night, so we don't need any additional sleep deprivation. We've lit candles and asked it to leave us alone, but it keeps happening.

My husband and I do not drink or do any types of drugs, and neither does my mom, so I don't think we are all cray-cray here. We are not into the occult or superstitious. We don't have pets besides fish. We have a very tiny attic but the noises only happen from downstairs from the 2nd floor, and when we are upstairs it sounds like heavy footsteps next to us nothing coming from attic. And we had the attic checked by a handyman and nothing is up there.

Any advice or experience?