Developer building high-rise behind me-want to buy my twin duplex

[TJ H.]

Hi,

My sister and I own a twin duplex near Philadelphia, PA. The other (half of?) twin is own by someone else - and it's also a duplex, owner occupies one unit, other unit is rented out. Our twin duplex is rented out and we like both of our tenants as they're dependable, stable, and relatively long-term, at least for the next 3-5 years. Our location is near transportation so an easy commute into Philly. 

A developer is now building a big apartment building behind us. Now some of this info was relayed to me (I no longer live near the area) and this is what I know, relayed by the other twin's owner:

Developer started to dig down into the ground and realize it's a high water line area. So they will be installing "several" industrial-strength water pumps/sump pumps.

Developer approached my neighbor (the owner of the other half of the twin) and said he's looking to buy both our properties so he can tear it down. He apparently let slipped that his plans actually/accidentally encroach on our garages in the back of our properties.

The other twin's owner want to sell. He has some experience in construction, and he explained:

- Our properties flood easily (minor but our sump pumps do turn on whenever it rains hard) due to the area being a high water line area - hence why everyone in the area has a sump pump.

- This big building will go up (& they're building a basement too) - and it will pump all the water out to the surrounding properties whenever it rains. There's no way our sump pumps will be able to handle the regular water we already get PLUS the additional water from the high-rise as well.

- He has a finished basement and he does not want to handle the hassle. Our basement isn't finished but we do have laundry down there plus storage.

- If the developer only gets one twin (or 1/2 of the house) then he will just rent it out. (Not sure what the game plan is here... wait it out until we sell as well?)

- If we both don't sell, and we suffer water damage, it would be costly to pursue for damages, and doubtful that we'd get anything <-- neighbor's opinion.

I'm looking for some advice or direction on where to go from here? I'd like to get some a second opinion but I don't know where to start.

We converted from oil to gas when we bought it in early 2015. We did a 15 yr mortgage so we've built some good equity. We have great tenants that more than cover our monthly PITI.

- If we stay, and there is water damage... what then? Get an industrial strength sump pump?

- If we sell, can we take the appliances out of there since he wants to demolish it? Can we salvage the new system we installed when we converted from oil to gas? I know we need to get an updated evaluation of our property since we did renovated one of the bathrooms and did the oil to gas conversion.

If you've read down this far, thank you!

Any advice will be greatly appreciated!