The ideal for a timing chain is usually set so that there is about 1/2 inch of vertical play in the chain. The idea is that when the cranks rotate any slight imperfections in the rings will still permit them to spin freely. If the eccentric is adjusted to too tight a tolerance and the rings are slightly out of round the chain may bind or actually derail. The other side of the setting is that a chain set too loosely may also derail itself under load.

If you take some time adjusting the eccentric and turning the cranks while the bike is held off the ground (preferably in a repair stand or even hung from the rafters in your garage) you'll be able to observe just how round the rings are and then decide how much play you want to establish.

Some tandem owners over-tighten everthing. I was guilty of this sin many times as a younger mechanic, but I learned over the 20 years I spent wrenching that "tight enough" is not too tight. Today torque wrenches make it a lot easier to establish "tight enough".

As for over-tightened crank bolts, they are a plague on humanity. There are any number of methods for getting them freed up: heat, carefully applied of course; penetrating lubricants; long torque assists etc. In every case be careful that the socket you are using is a very good fit so that you don't add to your misery by ruining the head of the crank bolt.

First shot? Use a long torque assist as you did with the cassette lock ring, being careful to control as many variables as possible, and making sure that you are indeed turning counter-clockwise. (I once broke a really good wrench by turning the wrong way, after breaking off the bolt head...That was a long day, but I never made the same mistake again.) Having a friend hold the bike upright will help. And, for the survival of your knuckles, make sure that you are carefully lined up with the wrench so that a suddenly loosened bolt does not send you off-balance.

Heat? Sometimes boiling water will help to free stuck bolts, but you may not want to try this because of the potential for scalding and then water everywhere. You might even end up dissolving grease in a sealed unit, so this is not necessarily a good idea unless you don't care about those bits. A heat gun can be useful, but again be careful because you don't want to get too much heat too near those lovely cranks. With really nice cranks and a good paint job on the line, heat should be a last resort.

Penetrating lubricants take time to work. The risk is that you may have too much oil getting into a sealed cartridge or other bearings so, care and patience again.

And, if that bolt is really tight you may have trouble with the crank removal too. Make sure you remove any washers before you apply the crank removal tool. It would be a shame to strip out those threads...a tiny bit of grease on the crank threads may help to get the crank removal tool well set. And, check to make sure that the threads on the tool are well lubricated too.

Good luck and check back to let us know how it goes.