there are people (like me) who have learned to be relatively independent from model No. (number), or I/O pins.
model No. is not that relevant, as for PIC, most code can be ported among them (at least, upwards).
also I/O pins can be expanded, even on 8-pin PICs.
you can generate AC, if you decouple from system ground.
just alternate two pins, first 1/0, then 0/1.
but this is not covering your requirement to generate sinoid waveform.
for this purpose you need external D/A. I do not know maybe you could also feed it in a way that it will produce negative voltage, at least for a few mA.
for larger current you need external negative voltage potential.
simple D/A can be built just from a few resistors, if you do not require high precision. otherwise you'd have to use dedicated D/A IC, which often also can accept external supply voltage.
the D/A IC is then driven by a pattern from a lookup table.
it is not always require to calculate the sinus explicitely directly on the PIC.