brass to cast iron threaded connection leaks

I have a drop ear elbow in brass such as the one shown here (it is brass). I was testing for leaks and all the sweated joints are fine, and all the pex joints are fine, but the threaded connections are leaking.

I have chromed iron pipes that are going to stick thru the drywall and connect to shutoff valves below sink and for toilet. I put about three wraps of teflon tape around the iron pipe and threaded it on with a pipe wrench. They are quite tight ( I was kind of worried about doing it too tight, but not really sure how hard to do it). When the water is turned on it leaks, not a spray just a drip. I tightened the sink pipes up months ago and they actually seemed not to be leaking (elbow to iron), but the shut off valves threaded connection did leak. So I have three shut off valves threaded to the iron that leak and one brass to iron connection that leaks.

Are they too tight? What kind of torque should one use? If I try some thread sealant will it work better? When I searched on here I read that some has silicon in it. That seems like it would certainly seal quite well if it was let dry before being pressure tested.

Should one wait to test threaded fittings for a few minutes? I know PEX fittings need to shrink. I would not have imagined threaded fittings need to wait before being checked, but the fact that the ones that were sitting there for a month did not leak made me wonder. I have read a lot of things that are confusing, some say that tight connections are necessary to deform the metal and make it seal well, others say that is true only for brass and not iron. Others don't say anything.

I appreciate any help.
Scott

edit:Title should just say iron not cast iron I connected to the cast iron sewage today and have it on the brain I guess.

Three full wraps of teflon tape on the nipple and some teflon pipe dope after that on the taped threads will have you leak free.
You can get these type of fittings pretty tight without worrying about cracking the brass drop ear. As long as the wrench you are using is not longer than 14" you should be alright.

kingsotall thank you for you help and especially about not worrying too much about over tightening.

It is just a 12 inch wrench, but the pipe started to make a squealing sound as I turned it near the end and I thought that might indicate it was getting too tight. I will pick up some pipe dope at the store and give it a go.

pipes

IF they are really steel pipes get rid of them and get chrome plated brass nipples. Tighten them as far as necessary to stop the leak. I would use pipe joint compound instead of tape, but that is just a personal preference.