My answer is no. Your tank is overcrowded. I'm sorry but unless you get rid of the TSN, then no clown loaches for you. You cannot try to mix the JD and oscar either. Consider the adult size and growth rate, not the current size when stocking your tank.
its like this dude you gonna get flamed by everyone by mentiuoning a 75 gal tank. A tsn can grow upwards of 6 foot in lenth yes yes i no it takes a while for that size. But in under a year your tsn will be pushing the llimits for your tank. Ide bet in 12 months it will be able to tuch the front and back of your tank. Try a lima shovlenose catfish . Not as cool looking but stays alot smaller then the tsn,the jd and oscar can live together in harmony but the oscar gonna outgrow it they poop alot. and are alittle bit on the dirty side of fish. Get you a 75 gal. a lima you oscar and jack you should be fine
i would suggest that there may be issues on the jd/oscar front, depending on the personalities of the individual fish. A 55 is barely big enough for a single oscar or jd. Oscars can be quarrelsome but jds tend to just be plain violent, so your o may have a little trouble on that front. In terms of the shovelnose, by all means in the right size tank have it with full grown Oscar and JD, but why stress the fish in a smaller than adequate tank when you could just wait to get the right size? I would go no smaller than 75 gallons for just the O and JD. GL