I have found it can be quite difficult locating burials -
First of all check the National Burial Index in case you get lucky. Google for any Monumental Inscription transcriptions online in the relevant areas/churches anything which will narrow down your search.
You have death certificates which is a great start as you have exact dates to search from.
If you think they could have been buried in local churches then you can see if the parish records are deposited with the local archives. Scunthorpe library may hold some I don't know. If the parish records have not been deposited you may be able to book an appointment with the vicar to view the records - be warned some charge serious money others none at all. They may say they will check for you for a fee. Always worth checking any monumental inscriptions in the Archives if any have been transcribed.
Also local paper archives (again the Library?) can be searched for any obits or funeral announcements.
If they are buried in a municipal cemetery, and you have already found where these are kept, then give them a ring. See if you have to make an appointment - pay to view them - or if they do the searching for you. Again you have a head start as you have the dates of death.
Any research you can do beforehand to organise it will be worthwhile.
Google and check the NBI
Source the locations of parish and municipal records
Spend some time on the phone in case you need to book in advance
Find out if you can search yourself or if they do it for you.
Take all your certs with you on the trip.
Check all locations of churches/graveyards/cemeteries before you go.
Find out if it will it cost you anything.
I am not an expert but I hope this helps.
Tressle