Titans return was expected - I believe they are operating it now in place of the EXT route which I think has now ceased. Jet2 & Titan were not competitors on the mail routes as they formed a joint company to run the routes a number of years back.
On the 757s - maybe having 2 spare in Manchester is a useful support if things go awry with the A330 this summer..... (slight overkill in seat numbers but if the 738's are leased it's probably cheaper to have the 752s sat on standby.)