If not I have other arrangements for them but I would like them to be able to go into my other 50 and not into a 30 gallon tank.

Well, there's only one way to find out I guess...

If there is algae and driftwood in the 50 gallon tank, and the shells for the shellies are at the other end from the driftwood, the two will be OK full grown. Juvenile BN's would be attacked.

Absolutely fine, I have kept them together myself. Just add some decorations in the corners or back for the plecs to hide and hang amongst and lay out tons of shells in the open space - all set.

Also the affect of driftwood in a tank is mild and in ph 7.5 and up you would need a tonne of it to make a difference. pets question and answers,www.5d2d.com

I don't know about BN fry because they did not breed, but the shellies only protected the immediate nest area, they are not overly aggressive and are not the type of cichlid to chase fish across the tank... Usually. The fry are so well protected in their shell piles and the BN never gave them the time if day. That was my experience, the tank set up for about 4 years.