There is no substitute for getting a pukka Alfa diagnostic on her; do a search on the forum for Alfa fault codes. This will give you a good idea what the issue is; unfortunately, it may still only be a guide to what the problem is, but then the expensive detective work can be kept to a minimum. Be aware that the crank sensor can be failing, then perform ok for a while before it fails, so you'll get poor starting, then ok, then total failiure to fire up. Fortunately the crank is the easier of the two to swap out; you'll find it on the firewall side of the engine block, very close to a large casting; take your undertray off, jack her up ( safely support the car), and you will be able to get to it with the star (Ribe) drive fixing ( there's only one holding it on) but make sure you get the old rubber O ring out before you fit the new unit. I found I had to remove a small amount of the plastic casing on the replacement before it would fit properly( compare your new Bosch sensor to the old one, and you'll probably see where to carve a tiny bit off), due to the proximity of the casting referred to above. If you need to change the Cam sensor, well, I'm afraid you are in for a fairly character building session of learning how to remove the aux belt, timing belt covers, etc before you get to the timing belt itself and the cam pulley wheel. At this point you face a choice; there is a way to leave the cam pulley wheel on, and get just enough space to be able to remove and replace the cam sensor ( you'll need to search the forum for this method), although I love a lot of the tips on here, I can't recommend this ( especially if you are a novice), if you don't get the method exactly right, there is a chance you could snap the small lug on the back of the cam pulley wheel when you tighten the bolt back up or dent the thin strip cast into the wheel with the cutout the sensor reads and your timing will be ruined ( not to mention the chance of valve/piston contact on starting....expensive learning curve); hopefully you can view this as an opportunity to fit a new timing belt, water pump and tensioner; it's a false economy not too. Check out the how to guides in red at the top of the forum, but in my humble opinion it makes sense to get the tools to lock the crankshaft in the right position to maintain your timing, and tippex marks on every reference point you can find, to give you the best chance of getting back together correctly. If you have a problem with the pump( on the engine) there's a good chance it may be the sensor on the rear of the pump, attached with two Ribe bolts, (costs about £100), it isn't too difficult to do, but I wouldn't describe it as easy...! I found Diesel Jones recon pumps were the cheapest exchange units I could find ( good for injectors too). If cash is tight, then probably your best bet is locate the parts on eBay ( alfapartsonline is excellent, price/quality wise, even tho his kit is sent from Poland!!!), and find a good Alfa specialist who is happy to use parts you supply. It is possible to do this work at home, but a novice is ( even with the guides on here, and the right tools) going to find it one hell of a steep learning curve; there a numerous opportunities to make a real horlicks of it all. I'm not trying to freak you out, and apologies if this is a teaching you to suck eggs scenario, merely trying to let you know what you could be getting yourself into, if you think you can knock this off in a couple of hours in your driveway...
I would definitely start with a proper diagnostic, which ever way you go, but there is way to test the crank sensor at least with a multimeter, a search on here should bring it up, but as far as my duff old memory goes, no way to test the Cam sensor.
Hope this helps you, and best of luck