I’m a little confused, lets talk about the hive with the issue, are you sure the queen remained in that hive?
If so she should have continued laying, if there is nothing in the brood then she simply isn’t there. But even so the colony should have made a new queen from available eggs.
While a hive is best if it is queen right constantly two months is getting close to the limit for a strong hive to be queenless without brood being added.
The sour smell is ringing alarm bells, do an inspection as a priority ASAP checking for wax moth and SHB and the start of a slime out. That is the only cause of a sour smell unless you dropped one on her while she was bent over the hive and you tried to blame the bees.
If the frames are OK then as you are concerned about taking frames of eggs from the other hive then buying a queen makes a doable option. But only buy a queen you can pick up yourself, Australia Post at the moment is so slow she would likely be dead before you get her. A very small parcel from Parramatta to me took 21 days exactly. A mate had 5 queens posted from the gold Coast to Noosa 18 days and all were dead.
Keep me updated
Cheers
Peter