Something like that should be possible
To explain it with an example, suppose you have bought PE & CE option contract for the same strike. Let’s say that is the NIFTY 14450 strike expiring on 28th Jan 2021. Currently, the combined premium of those two option contracts is around 240 points. In case you want to have a combined premium stoploss at 230 points, then you can create an alert for it in Sentinel using the following Advanced Trigger condition -
(LastTradedPrice('NFO:NIFTY21JAN14450CE') + LastTradedPrice('NFO:NIFTY21JAN14450PE')) < 230
Alternatively, if you had sold both those option contracts and wanted to set a combined premium stoploss at 250 points, then you could create an alert for the same using the following condition -
(LastTradedPrice('NFO:NIFTY21JAN14450CE') + LastTradedPrice('NFO:NIFTY21JAN14450PE')) > 250