These are my answers,I am not a fan of either of the leads and don't know everything about tv world so if I say something wrong I will try to listen with an open mind and rectify my mistake.
Yes,bepannaah made its place in top 5 in the first week itself but after that it has only dwindled from 2.7 to 2.2 to 1.8 to further downwards,a project's fate depends on how well it does overall and not only on how it did in the initial weeks or days (another example - thugs of hindostan made 50 crores on its first day but after that the collections dropped severely and it will not prove to be a successful project).I know bepannaah does not start on time (a problem other shows face too) but I think(I am not completely sure about this so please correct me if I am wrong) in the initial 2-3 weeks at least it did start on time and still the ratings kept dropping.I am not blaming the actors for this,they did their part by bringing in initial numbers (specially jennifer who did this show immediately after beyhadh which gave her immense popularity) but after the initial week it is the drama and trp friendly content(for which the PH is responsible) matter.TBH this PH hasn't given many trp hit shows(last one was around 2007 i think - EHMMBH on star plus) so for me at least it is not entirely surprising that this show did not do well trp wise.
Yes silsila mostly did bad and that is precisely why it is being shifted to voot within 3-4 months of its launch,apparently it does well on voot (i think the writer said so)
I don't know much about the budgets,I will take your word for it if you say DEM's is more(I do think the combined pay of jenshad must be higher than that of shaheer sonarika but perhaps the sets are costlier for DEM).But I think we should keep in mind that DEM is a new show (only 2-3 months old) and colors must be willing to give it a chance,something it gave bepannaah too.There was a show on colors years back named rangrasiya which had high budget,more than adequate promotion and low ratings,colors gave it some 9 months too before pulling it off air.
About silsila shifting to voot and not bepannaah,again I don't know much about it but haven't there been rumours that bepannaah was offered this too but the leads refused (their choice entirely and no criticism for that)?
I know timing is a big problem for colors and I don't understand why they don't fix it,perhaps they thought that if we air one show on time of another then we can get audience of one show interested in another too?But this idea seems to have failed and should be dropped now I guess.I think BP should have been kept at 9:00 pm,9:30 has more competition.I think the reason given was that 9:30 is considered more love story friendly while 9 is family drama time.Is this true?Surely there must have been love stories which gave good ratings at 9 pm?