If you're going to go with some amplification and distribution, then I'd recommend tackling both in a single unit. That way you're only going to be adding one set of processing noise rather than two; one from the amp and one from the splitter.
Some might suggest a passive splitter in the loft. That's possible of course, but it's not the best way to use a passive. There are a couple of golden rules about distribution.
The first is that anything active such as aerial amps and distribution amps should live as close as possible to the aerial. The reason for this is so that the signal is as clean and has the best signal-to-noise ratio (SNR) possible before amplification. That makes sense when you think about it. Amplifying a 'dirty' signal is just going to make a bigger dirty signal. Getting the signal as close to the source as possible means there's less noise in it, and that means a smaller reduction in SNR when trading off quality for power.
Second, passive splitting is done as close to the receivers as possible. IOW, we don't use passive splitters in a loft.
The reason for this is a bit more involved but it is to do with the the signal level before and after splitting and the noise picked up as the signal travels down cable. The objective is to keep the signal-to-noise ratio as high as possible for as long as possible.
If I was to use say a 4-way passive splitter in the loft, then there'd be no additional noise from the splitter which is a good thing, but each signal output would be slightly less than a quarter of the strength of the original. Any noise picked up in the cable run to the display has a bigger percentage impact. Keeping the signal whole means that the same noise level picked up doesn't represent such a big part of the total signal. This means the SNR is better.
If I use some crude numbers to illustrate the idea:
100 for aerial signal, then pick up 2 for noise in the long cable run, then the percentage of added noise to total signal is 2/102 or 2% in round figures
Compare that to a 4-way (we'll ignore the insertion losses):
4-way split gives each output a signal of 25. Add the same 2 for noise. The percentage of noise to total signal is 2/25, or 8%. That's a much noisier signal as well as being weaker.
Delaying the passive split point for as long as possible means any noise picked up is a smaller percentage of the whole signal. Fixing the passive split point at some equidistant point between the TVs means shorter runs for the weakened signal, and so not as much noise is picked up when the signal is smaller.
Back to your loft then, going for a masthead amp and a powered splitter means two lots of processing noise. That's not good if it can be avoided. What you do instead is go for a 4-way masthead amp.
You won't need a huge amount of gain, so something like
this 0-20dB variable will more than cover the 7.5dB loss from a 4-way split and give you up to 12dB of additional gain to overcome the signal loss when it rains.
