Freewheel replacement for a touring tandem bike I have an older touring tandem bike that we use to go on long trips. The gear setup is 3x7. I noticed that we hardly ever use the smallest 3 cogs on the freewheel (of course together with the largest chainwheel). We also struggle on the climbs, so I would like to change the freewheel to help us on the climbs.
The freewheel setup is 13-30. I am thinking or replacing it with something like 16-36 or similar. The problem is that I haven't found a 7-gear freewheel with such a setup. The only freewheel with a better setup that I've found is the Sunrace MFM300 7DV. But the difference seems to be major only on the largest cog (30 vs 34).
This is the current freewheel:

Do you know where I could buy a freewheel with a better setup for climbing than this?
Or would you recommend that I do one of the following?

Change the chainrings - from what I see, I would have to
change all 3 of them, as the screws on the smallest chainring would
not allow changing it with a smaller one. Seems to involved for my
bike repairing skills.
Change the back wheel entirely to support a newer, cassette style type of cogs. One problem is that
the back wheel is also fitted with a drum brake on the left side, no idea how to
properly re-fit it on a new wheel. Also, I would like to keep as many original parts as posible on the bike.
Changing the wheel's hub to a freehub to support a casette. This has the
advantage that the bike will stay with most of its original parts,
but would be really involved. Again, might be difficult to impossible to re-fit the drum brake.

Advices welcome, I'm not an expert bike tehnician.
Chainring sizes: 54-48-40.
Current chainrings:

Chainrings' Bolt:


Update a few months later
I thought it would be useful for anyone having a similar question to have an update on this question after following the very good advices that I have received here.
What I ended up doing: I replaced the right side crank and chainrings for a lower overall gear. Unfortunately I couldn't replace just the chainrings, as there was no way to fit smaller ones on the existing crank. I only replaced the right side because this is a tandem and on the left side there's the connecting chain. Finding a complete tandem crankset is difficult and more expensive, but fortunately replacing just the right side of it did the trick. The only difficulty was finding a crank with exactly the same length as before.
I also replaced the chain, as it was very dirty. Unfortunately this led to the replacement of the freewheel, as the new chain was slipping on the old one. I guess it was also worn out.
Although I couldn't avoid an upgrade spiral, I managed to bring down the gear ratios so now we can enjoy more difficult rides.
Indeed, replacing the crankset was quite easy and I might actually do it again if I notice that we need an even lower gearing.
Thank you for the advices!
I think in this situation, to avoid an &quot;upgrade spiral&quot;, you will be better off changing your chainrings. Chainrings are not overly expensive and probably won't require new derailleurs or shifters.
I have been known to take apart freewheels and change the cogs. I've even re-spaced them or changed the numbers of speeds. But if you want an overall lower gear, you should probably change your chainrings.