I don’t know how your family would define relaxing…
Beds - For my family, it is not a relaxing vacation when the kids can’t sleep well because that translates to bad attitudes during the days. By the time they were 10ish (now DD24 and DS22), they had a hard time sleeping on a sofa bed. So, when looking for vacation rentals, we always looked for ones that sleep at less 5, even though there is only 4 of us. Entering 4 tends to give us 1 bed and a sofa bed. So, a relaxing vacation means that everyone needs to sleep in a bed!
Space and Bathrooms - Last year, we got to stay in a couple of vacation rentals where each kid had their own room! It was relaxing to have the space! Hotel rooms are small, many without couches. And having more than one bathroom is so, so nice! It’s a time saver and we all have better attitudes when we can use the bathroom when needed!
Park Days - A WDW vacation is not necessarily “relaxing”. I know; DH and I just came home from an 8-night one on Sunday. RDing to nearly closing the park is tiring. And all that walking! And you will have humidity in July! If you take an afternoon break, staying onsite could be convenient.
Saving money at Disney is a big topic. Everything is pricey!
Food is expensive. Does your family need a hot breakfast everyday? Or can they do bars and other packaged items? Factor this into your housing.
I know families who bring their own sandwiches for lunch and dinner for their entire Disney trip. My family wouldn’t say it is relaxing to be eating a sandwich on the bench with other guests watching them. But we have done a few brown bagged lunches to save some money for TS dinners.
So, do factor in the food and snack costs because they add up really fast for a family at WDW! You can find prices on the menu. And offsite food is a whole lot cheaper! We had this Cuban Roast Pork with 3 sides for $12 before tax! It was enough food for two of us.
It is very possible to rent an offsite vacation rental, rent a car, and rent a room onsite for 5 people for a night (to get the Disney perks for arrival and departure days) for close to the same price as staying at an onsite resort once you add up all the projected costs. Some Liners here have elaborate spreadsheets to budget!
In 3 trips to WDW, we stayed onsite once; at a good neighbor hotel once, using lyft and hotel shuttle; and offsite once, renting a car and renting a room for once night.
Do consider your family’s overall vacations needs, touring style, and budget together before you decide. Have a magical, relaxing vacation!