Yes, you can replace them yourselves.
Take pictures, several of them, as to where the cables go. When people have problems after changing batteries it's usually because they didn't hook up the cables the same way they took them off. They just take off all of the cables, pull the batteries, put the new ones in and then have no idea how to hook up the cables again and do it wrong.
Having said the above, depending on how your batteries are in the battery holder, it's safest to only replace one battery at a time to help get the cables back in the right place.
If he's not used to battery work, have him tape the end of the wrench that goes in his hand so that it doesn't touch anything else and create a spark.
If you put your RV into storage you should be disconnectiing the negative battery cable on both sets of batteries to prevent then from draining and ruining them. The battery disconnect switch someplace up front in the RV does not disconnect everything. The best thing is to have someone connect a real battery disconnect switch, on both sets of batteries, in the cable next to the batteries. This way you don't have to take the negative cable off when you aren't using the RV.
Bill