I'm not a gull expert, but I think the most likely white-headed taxa in Mumbai should be heuglini and barabensis. Both are currently treated as part of Lesser Black-backed Gull. Given that the 2nd and 3rd pictures look fairly pale above, maybe barabensis? But there's more than one bird here, so they might not all be the same. The wing pattern may be useful for an expert to comment.
The pipits look like Paddyfield I think.
For the terns, the one on the right looks like Common to me, from structure and head pattern. But the one on the left is slightly different and I'm not sure if it's another Common or a different species.
This is a really difficult set of photos, all with difficult species groups to ID. That may be the reason that there haven't been many responses so far!