Can i put them together as one

If I am understanding what you are trying to do here, the way create scores like this is not to do so in two separate as you have. Instead, you should simply create one score that has both parts in it, then go to Style / General and turn on the "hide empty staves" option. This will automatically create the look I assume you are trying to achieve - single staff for the first violin at first, then expanding to two staves when the second violin enters.

So, what I'd do at this point is append 16 bars to your part A, also add the second staff, then copy and paste the contents of your part B into those new bars. Then turn on the hide empty staves option.

To add a part to a score, go to Create -> Instruments or Press i

Create two instruments. Once you have entered all the note, Style -> Edit General Style -> Score and check Hide Empty Staves.

I am not sure how to create a piano (two staves) at the start of piece for 10 bars, then followed by tenor voice (8 treble), voice bass plus piano (two staves) for rest of piece. Do I create tenor, bass and piano in the set up of the file and enter the piano notes for 10 bars then hide tenor and bass bars. Similarly, if I decide to have the same situation in the middle of the piece? Is this the accepted way to do this? But will the hidden bars (tenor/bass) leave an unwanted space?

I ask the above since I have found that if I delete, for example, the tenor top line, to see if that will work, deleting the tenor bars, deletes all the measure below!