TSR2.
I am going to presume you are from Australia? With the airline i work for, the 737-300's are just about out the window anyway, getting too old.
As far as i can remember, with our airline, 3 Flight Attendants and one 'Purser' is the standard number of operating crew for most legs on this aircraft. The Purser is responsible for L1 door, one flight attendant is responsible for R1 door and two Flight Attendants are responsible for doors R2 and L2 (senior F/A). Passengers seated at the overwing exits are briefed and responsible for opening the two overwing emergency exits.
All crew wouldn't be allowed online if they were proven to be competent in dealing with all aspects of aircraft safety, including emergency procedures, equipment, first aid etc and ALL crew are tested and examined on this every 6 months for their whole career. What a lot of passengers may not understand is that each F/A position has certain duties that they're responsible for onboard and when you're new, this can be a little confusing/daunting until you get the hang of things, especially when sector to sector the service can be different based on the time of the day and whether or not you're working in economy or business class, also very daunting when the other crew know what they're doing and are working at 1000km an hour. Everyone when they first start needs guidance with the service flow etc, they try and teach you from a book, but when you're up there learning it's very different. it's up to all crew to help with this.
99% of crew have had very little practical experience in putting their training into action (except during training), but trust me, it's all there when you need it. As i said, you can rest assured, ALL crew need to display that they are aware and competent in dealing and operating all aircraft equipment.
With us, the old way for training was that new crew would be assigned an in-flight trainer where they would do the same roster as their trainer for a month, they would also need to fill out a competency journal in which they would have reviewed at certain periods by their manager to make sure they're up to scratch etc. Unfortunately now, that doesn't tend to happen, but new crew are usually given "supernumery" flying, where for two or so flights they are an additional crew member in addition to the standard crew complement, they can choose to participate in the service etc or just watch, most participate. What you may have experienced is that these crew were unfortunate not to have any training flights, but were put right into it, this is fine, except this flight may have originally been allocated the standard number of crew and then one gone sick last minute, couldn't get anyone else so were approved to operate on minimum crew, this does happen. (as said, in Australia, the number of crew normally operating on a 737-300 is 4 including the 'Purser').
I don't think you have anything to worry about in regards to the lack of experience etc in aircraft safety, equipment etc with new crew, they would all know what to do. However it can be quite a scarey thing for new crew to have to work on an aircraft (unfamiliar environment in itself if you haven't done it before) and have to deal with every day things. It is all completely different up there than what you do in training.
I suppose it really depends on what they were talking about? If they were literally saying they don't feel comfortable with something to do with equipment etc, then maybe it should have been brought up. Crew (and a lot of crew aren't) need to be aware of how loud they're talking and what they're talking about as if you're talking in the galley's, you're voice actually projects into the cabin. I quite often feel embarrassed and tell other crew to turn the volume down due to being able to hear them 6 rows into the cabin!
Oz