Be patient, get to know your local and online REI. Buy stuff on sale or clearance after you have visited the store and have a good idea what the gear is like. Be sure everyone climbs into whatever gear they think they want to check real world size.

An REI 4 season tent on sale. Push if necessary to get the tents you like set up so everybody can get inside. Buy a tent rated for AT LEAST one more person than will stay in it - and then strongly consider getting a tent rated for AT LEAST two more persons than will stay in it. Consider a separate tent for the kids.

REI-sourced, do-it-yourself layered sleep systems. Start with a Travel-Sack and later look warmer sleeping bags into which the Travel Sack can fit. Maybe consider a bivy into which the sleeping bag can fit. Maybe a liner that can fit into the Travel Sack. Buy the parts on sale.

REI-sourced best sleeping pads you can afford in the biggest sizes that collectively work with your tent. A self-inflating Term-A-Rest is worth its weight in whatever you hold dear. Try to get them on sale.

Include the kids and spouse in the process to the extent they are willing; listen to them. Have fun.