Re: using both tie and slur between two chords
If you already have a chord with all the ties activated, then select the chord, hit the / key to remove all ties. Then remove the chord member that needs a tie and put it back into the chord with the tie activated.
NWC 2.51 has made this easier. You can right-click while hovering over any notehead on the selected staff. This brings up a context menu that allows you to edit all the properties of that notehead except for its position.