P&L formula

You will get all these values in positions response itself. For example

"net": [{
"tradingsymbol": "NIFTY15DEC9500CE",
"exchange": "NFO",
"instrument_token": 41453,
"product": "NRML",

"quantity": -100,
"overnight_quantity": -100,
"multiplier": 1,

"average_price": 3.475,
"close_price": 0.75,
"last_price": 0.75,
"value": 75.0,
"pnl": 272.5,
"m2m": 0.0,
"unrealised": 0.0,
"realised": 0.0,

"buy_quantity": 0,
"buy_price": 0,
"buy_value": 0.0,
"buy_m2m": 0.0,

"day_buy_quantity": 0,
"day_buy_price": 0,
"day_buy_value": 0.0,

"day_sell_quantity": 0,
"day_sell_price": 0,
"day_sell_value": 0.0,

"sell_quantity": 100,
"sell_price": 3.475,
"sell_value": 347.5,
"sell_m2m": 75.0
}]

So the formula is

pnl = (position.sell_value - position.buy_value) + (position.quantity * lastPrice * position.multiplier)

You should be using last price you get from ticker to calculate live positions pnl. This exactly the same thing going on Kite web and Kite apps.