Voters lists are unlikely to contain any useful information. Universal male suffrage in the UK didn't happen until after WW1; before that there were a variety of property requirements so no, it is not a useful source of information for poor people. The area where you should start looking is in the church records for baptisms, marriages and burials for Pembrokeshire, which are the only surviving data prior to 1841. These are held at the County Records Office in Haverfordwest. This office is currently engaged in a change of premises and will not reopen until the end of March. It is possible that the staff in this office would carry out a search for you if you can give them as much information as possible. I have recently been informed by another family historian that Pembrokeshire parish records are now online at Findmypast. I haven't been able to check this since I don't have a subscription to FMP and normally use it when I go to the Haverfordwest office.
Individual parish records vary widely in standards of preservation and legibility. These records apply only to the Anglican churches; if your ancestors were Methodist or Baptist (very common in Pembs) they would have been married in an Anglican church, but baptised and buried in their own non-conformist churches, for which records are not widely available.