@gamba
There are a couple of design decisions that you will need to make in the future regarding your set up If you have IP overlap we wont discuss all of them for your problem but you should be aware of it so i shall mention it below.
If you want to limit the amount of OSPF advertisements into your Area (non-backbone) then highly recommend making it a stub. Considering you are redistributing routes into your Area as you have an ASBR then i recommend NSSA totally stubby. In this way you will not see any external routes from the backbone and you will get a default route injected into your Area only.
That should simplify the routing quite a bit within your area. You will not see the conflicting prefixes from the backbone as your area only knows about the intra-area routes and a default route from the ABR. External destinations injected into your area will be by your ASBR in which case routing to those external areas is handled all within your Area.
The other design decision is to break up these OSPF areas with BGP. You run eBGP between you and the other site. Run OSPF within the LAN(assuming its larger enough to warrant that). In this way, BGP being a policy-driven protocol more so then a routing one, you are able to control what gets announced by you and the benefit of steering traffic the way you want it.
That said, as i mentioned, you can only filter routes into an Area or routes leaving an area. Thats it.
Create your route-maps in pfsense by going to Services > FRRGlobal Settings > Route Maps
Then apply that route-map on your ASBR or your ABR under
Services > FRR> OSPF> edit Areas